CN102570864A - 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 computational methods of a kind of modularization multi-level converter

Technical field

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

Background technology

In recent years; For satisfying the demand that economic growth increases supply of electric power day by day; The voltage source converter (Voltage Source Converter is called for short VSC) that can turn-off power electronic device based on large power all-controlled type is widely used in high voltage direct current transmission (High Voltage Direct Current the is called for short HVDC) technology; And obtained good operational performance, be referred to as flexible DC power transmission technology (VSC-HVDC).But; The loss of this system (adopting the flexible DC power transmission technology) is far longer than the loss of traditional DC transmission system; This mainly is because the flexible DC power transmission technology adopts bigger converter loss to cause; Especially two level, three-level voltage source converter, though its topological structure, control strategy are comparatively simple, switching frequency is high, the converter loss is bigger; This also becomes its major obstacle that is applied to high-power long-distance transmissions, so fall the damage measure and will have the important engineering meaning what the loss characteristic of voltage source converter was furtherd investigate and proposed to be correlated with.

A kind of novel voltage source converter topology---characteristics such as modularization multi-level converter (MMC) is flexible because of its control, switching frequency is low, loss is little just progressively are applied in the flexible DC power transmission engineering.The loss characteristic research of modularization multi-level converter also becomes one of research content of flexible DC power transmission technology; Existing loss computational methods are mostly to two level voltage source converters, and are considerably less about the research that the modularization multi-level converter loss is calculated.Compare with two level converters; The topological structure of modularization multi-level converter, control mode and loss characteristic all have very big-difference, and only some can apply in the loss calculating of modularization multi-level converter existing two level converter loss computational methods.

On the one hand; Particularity because of modularization multi-level converter topological structure, operation mechanism and control mode; Synchronization flows through the electric current of upper and lower bridge arm IGBT module maybe be different, though also can release the current value of modularization multi-level converter upper and lower bridge arm with the method for theory analysis and empirical equation, still 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 just the upper and lower bridge arm of the every phase of modularization multi-level converter has a lot of SM modules, need measure the electric current that flows in each SM module two IGBT devices and two fly-wheel diodes (FWD) device during computed losses, also need detect the conducting state of each device; If the loss of manual calculation converter, workload will be very huge; Such as the U.S. Trans Bay Cable Project (TBC engineering) that has 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, and wherein 198 SM modules put into operation and constitute 199 level, other 18 SM module redundancies; If measure its loss; Must measure the electric current that obtains the individual IGBT of 3 * 2 * 216 * 2=2592 (wherein 3 be meant the MMC three-phase bridge, 2 * 216 be the number of the single-phase brachium pontis SM of MMC module, last 2 be IGBT device number or fly-wheel diode device number in each SM module) and the electric current of the fly-wheel diode of number equally; If but adopt the method for online detection; Only need to give each device the inside to increase corresponding electric parameters measuring point, build the corresponding calculated module, through certain algorithm; Just can rely on computer; In very short simulation time, realize the real-time calculating of loss in the emulation quickly and easily, can reduce workload greatly.So will seek a kind of loss computational methods that can be applicable to any situation; Still there is not document that the online loss computational methods of modularization multi-level converter are carried out systematic research at present; So; Along with the actual extensive use of engineering, select suitable simulated environment PSCAD/EMTDC, doing further investigation to the online loss computational methods of modularization multi-level converter has urgent demand property and necessity; This will not only have the important in theory innovative significance, also have important actual construction value.

Summary of the invention

The present invention is directed to above-mentioned defective and disclose the online loss computational methods of kind modularization multi-level converter.It may further comprise the steps:

1) obtains A phase brachium pontis current i through measuring _a, B phase brachium pontis current i _b, C phase brachium pontis current i _cWith the working temperature t of current environment, calculate the on-state loss of an IGBT, the 2nd IGBT, first fly-wheel diode and second fly-wheel diode in each SM module then:

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

3) calculate the total on-state loss P of IGBT through the 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.

Said step 1) specifically may further comprise the steps:

11) from product description, obtain following four curves: the collection emitter voltage V ' of IGBT when temperature is 25 ℃ _CEWith collector current I _CRelation curve, the collection emitter voltage V of IGBT when temperature is 125 ℃ _CEWith collector current I _CRelation curve, the forward conduction voltage V ' of first fly-wheel diode when temperature is 25 ℃ _F-DC Forward Current I _FThe forward conduction voltage V of relation curve and temperature first fly-wheel diode when being 125 ℃ _F-DC Forward Current I _FRelation curve;

12) the collection emitter voltage V of an IGBT when temperature is 125 ℃ _CEWith collector current I _CRelation curve in, obtain following N group data through 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 _CENBe an IGBT collector current value to be I _C1-I _CNThe time 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 the high order curve match in MATLAB, an IGBT collection emitter voltage V when obtaining temperature and being 125 ℃ _CEWith collector current I _CRelationship;

According to formula: R _T1=V _CE1/ I _C1, R _T2=V _CE2/ I _C2... R _TN=V _CEN/ I _CNObtain: when an IGBT collector current value is I _C1-I _CNThe time the one IGBT the 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 the high order curve match in MATLAB, the on state resistance R of an IGBT when obtaining temperature and being 125 ℃ _TWith collector current I _CRelationship;

13) the first fly-wheel diode forward conduction voltage V when temperature is 125 ℃ _F-DC Forward Current I _FRelation curve in, obtain following M group data through 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 first fly-wheel diode, V _F1-V _FMBe that DC Forward Current value when first fly-wheel diode is I _F1-I _FMThe time first fly-wheel diode the 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 the high order curve match in MATLAB, the first fly-wheel diode forward conduction voltage V when obtaining temperature and being 125 ℃ _FWith DC Forward Current I _FRelationship;

According to formula: R _D1=V _F1/ I _F1, R _D2=V _F2/ I _F2... R _DM=V _CEM/ I _CMThe DC Forward Current value that obtains when first fly-wheel diode is I _F1-I _FMThe time 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 the high order curve match in MATLAB, the first fly-wheel diode on state resistance R when obtaining temperature and being 125 ℃ _DWith DC Forward Current I _FRelationship;

14) four curves in the step 11) are carried 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 alpha of the on-state loss of an IGBT and the 2nd IGBT _TJunction temperature alpha with the on-state loss of first fly-wheel diode and second fly-wheel diode _D, in the above-mentioned formula, t is the working temperature of current environment;

15) in curve fitting module, calculate the threshold voltage V such as real-time on-state of an IGBT through following formula _CEX, first fly-wheel diode 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 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) with V _CEXAnd R _TXThe following formula of substitution is through calculating the middle on-state loss P of an IGBT _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 the 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 _EFBe the threshold voltages such as on-state of IGBT, I _EFBe the equivalent electric current of the on-state of IGBT,

Be 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 _EFFunction for t and i;

With V _DXAnd R _DXThe following formula of substitution is through calculating the middle on-state loss P of first fly-wheel diode _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 the above formula, the upper and lower bridge arm electric current that flows into modularization multi-level converter is i, V _DFBe the threshold voltages such as on-state of fly-wheel diode, I _DFBe the equivalent electric current of the 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 _DFSFunction for 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, through step 11)-step 16) draw the threshold voltage V ' such as 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 second fly-wheel diode _DFSMiddle on-state loss P with first fly-wheel diode _DFSComputational methods identical, through step 11)-step 16) draw the threshold voltage V ' such as real-time on-state of second fly-wheel diode _DX, second fly-wheel diode real-time on-state substitutional resistance R ' _DXMiddle on-state loss P ' with second fly-wheel diode _DFS

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

19) calculate the on-state loss P of an IGBT through following formula _EF, the 2nd IGBT on-state loss P ' _EF, first fly-wheel diode on-state loss P _DFOn-state loss P ' with second fly-wheel diode _DF:

P _EF＝s1×P _EFS

P′ _EF＝s2×P′ _EFS

$P_{\mathrm{EF}}^{\′}=s2\×P_{\mathrm{EFS}}^{\′}$

P _DF＝s3×P _DFS

P′ _DF＝s4×P′ _DFS。

$P_{\mathrm{DF}}^{\′}=s4\×P_{\mathrm{DFS}}^{\′}.$

Said step 18) specifically may further comprise the steps;

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

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

Said step 2) specifically may further comprise the 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 with variation of temperature, its computing formula is following:

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

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

In the above-mentioned formula, E _Sw1Be the energy loss in the switching process of an IGBT when meeting the following conditions: an IGBT supply voltage V _CcBe reference voltage u _Ref, the rated current electric current is reference current i _Ref, junction temperature is 125 ℃; E _Sw2Be the energy loss in the switching process of an IGBT when meeting the following conditions: an IGBT supply voltage V _CcBe reference voltage u _Ref, rated current is reference current i _Ref, junction temperature is 25 ℃; E _Sw1And E _Sw2All know through the product description of an IGBT;

E _Rec1Be the reverse recovery energy loss of first fly-wheel diode when meeting the following conditions: voltage is reference voltage u _Ref, DC Forward Current is reference current i _Ref, junction temperature is 125 ℃; E _Rec2Be the reverse recovery energy loss of first fly-wheel diode when meeting the following conditions: voltage is reference voltage u _Ref, DC Forward Current is reference current i _Ref, junction temperature is 25 ℃; E _Rec1And E _Rec2All know through the product description of first fly-wheel diode;

22) the switching frequency measurement module obtains the switching frequency f of an IGBT through the number of measurement unit's SM module trigger impulse in the time _ST, the switching frequency f of first fly-wheel diode _SDBe the switching frequency f of an IGBT _STHalf the;

23) calculate the switching loss P of an IGBT through following formula _SwTReverse recovery loss P with 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 the above-mentioned formula, U _CBe 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 first fly-wheel diode under the maximum junction temperature;

24) the switching loss P ' of the 2nd IGBT _SwTSwitching loss P with an IGBT _SwTComputational methods identical, through step 21)-step 23) obtain the switching loss P ' of the 2nd IGBT _SwT

The reverse recovery loss P ' of second fly-wheel diode _SwDReverse recovery loss P with a fly-wheel diode _SwDComputational methods identical, through step 21)-step 23) obtain the reverse recovery loss P ' of second fly-wheel diode _SwD

The total on-state loss P of said IGBT _TconBe all SM module I GBT on-state loss sums of modularization multi-level converter, the 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 said fly-wheel diode _DconBe all SM module fly-wheel diode on-state loss sums of modularization multi-level converter, the fly-wheel diode on-state loss is the on-state loss P of first fly-wheel diode _DFOn-state loss P ' with second fly-wheel diode _DFSum;

Said IGBT master switch loss P _TswBe all SM module I GBT switching loss sums of modularization multi-level converter, the 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 said fly-wheel diode _DrecBe all SM module fly-wheel diode reverse recovery loss sums of modularization multi-level converter, the fly-wheel diode reverse recovery loss is the reverse recovery loss P of first fly-wheel diode _SwDReverse recovery loss P ' with second fly-wheel diode _SwDSum;

Said IGBT total losses P _TBe the total on-state loss P of IGBT _TconWith IGBT master switch loss P _TswSum;

Said fly-wheel diode total losses P _DBe 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 said modularization multi-level converter _ConBe the total on-state loss P of IGBT _TconWith the total on-state loss P of fly-wheel diode _DconSum;

Said modularization multi-level converter master switch loss P _SwBe IGBT master switch loss P _TswWith the total reverse recovery loss P of fly-wheel diode _DrecSum;

Said modularization multi-level converter total losses P _TotBe IGBT total losses P _TWith fly-wheel diode total losses P _DSum;

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

Beneficial effect of the present invention is: the first, and avoided among the MMC number of modules more effectively, the manual measurement complexity of calculation, workload reduces greatly, and is efficient and convenient; The second, through the associated electrical tolerance of real-time measurement system, realized the 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, very convenient in modularization encapsulation in actual engineering, save floor space, improve resource utilization, and this platform is output as all kinds of losses and loss ratio, straightforward, make things convenient for staff's observing system running status at any time.

Description of drawings

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

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

Fig. 3 is the curve fitting module functional schematic;

Fig. 4 is a switching frequency measurement module functional schematic;

Fig. 5 is a duty ratio measuring functions of modules sketch map;

Fig. 6 finds the solution the functions of modules sketch map for duty ratio mean value;

Fig. 7 is a loss computing module functional schematic.

Embodiment

Below in conjunction with accompanying drawing the present invention is done further explain.

Technical problem to be solved by this invention is when overcoming the system running state change; During such as the 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, the online loss computer general of a kind of effective, real-time modularization multi-level converter platform is provided

The present invention finds the solution module and loss computing module through switching frequency measurement module, duty ratio measuring module, duty ratio mean value under PSCAD/EMTDC, realize that the online loss of modularization multi-level converter is calculated.

As shown in Figure 1; Modularization multi-level converter by A phase brachium pontis, B phase brachium pontis and C mutually brachium pontis form; A phase brachium pontis is gone up brachium pontis mutually by A and is descended brachium pontis to form mutually with A; B phase brachium pontis is gone up brachium pontis mutually by B and is descended brachium pontis to form mutually with B, and C phase brachium pontis is gone up brachium pontis mutually by C and descended brachium pontis to form mutually with C, and A goes up brachium pontis, A mutually and descends brachium pontis, B to go up brachium pontis, B mutually mutually to descend brachium pontis, C to go up brachium pontis mutually mutually to descend being in series by n SM module of the 1st SM module to the of brachium pontis mutually 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 following: an IGBT who is parallel with first fly-wheel diode connects with the 2nd IGBT that is parallel with second fly-wheel diode, connects with capacitor C then.

Each SM module loss is divided into the loss of an IGBT, the 2nd IGBT, first fly-wheel diode and second fly-wheel diode; The one IGBT loss is divided into the steady-state loss of an IGBT and the switching loss of an IGBT again; The 2nd IGBT loss is divided into the steady-state loss of the 2nd IGBT and the switching loss of the 2nd IGBT again; The steady-state loss of the one IGBT is divided into the drive loss of an on-state loss and the IGBT of an IGBT; The steady-state loss of the 2nd IGBT is divided into the drive 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, and 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 the on-state loss and first fly-wheel diode of first fly-wheel diode, and the second fly-wheel diode loss is divided into the reverse recovery loss of the on-state loss and second fly-wheel diode of second fly-wheel diode.Wherein the drive loss of an IGBT and the 2nd IGBT is very little; Can ignore, so mainly the on-state loss of an IGBT, the on-state loss of the 2nd IGBT, the on-state loss of first fly-wheel diode, the on-state loss of second fly-wheel diode, the switching loss of an IGBT, the switching loss of the 2nd IGBT, the reverse recovery loss of first fly-wheel diode, the reverse recovery loss of second fly-wheel diode are calculated among the present invention.

The online loss computational methods of a kind of modularization multi-level converter may further comprise the steps:

1) obtains A phase brachium pontis current i through measuring _a, B phase brachium pontis current i _b, C phase brachium pontis current i _cWith the working temperature t of current environment, calculate the on-state loss of an IGBT, the 2nd IGBT, first fly-wheel diode and second fly-wheel diode in each SM module then:

Step 1) specifically may further comprise the steps:

11) from product description, obtain following four curves: the collection emitter voltage V ' of IGBT when temperature is 25 ℃ _CEWith collector current I _CRelation curve, the collection emitter voltage V of IGBT when temperature is 125 ℃ _CEWith collector current I _CRelation curve, the forward conduction voltage V ' of first fly-wheel diode when temperature is 25 ℃ _F-DC Forward Current I _FThe forward conduction voltage V of relation curve and temperature first fly-wheel diode when being 125 ℃ _F-DC Forward Current I _FRelation curve;

12) the collection emitter voltage V of an IGBT when temperature is 125 ℃ _CEWith collector current I _CRelation curve in, obtain following N group data through 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 _CENBe an IGBT collector current value to be I _C1-I _CNThe time 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 the high order curve match in MATLAB (MATLAB is the abbreviation of matrix experiment chamber (Matrix Laboratory)), an IGBT collection emitter voltage V when obtaining temperature and being 125 ℃ _CEWith collector current I _CRelationship;

According to formula: R _T1=V _CE1/ I _C1, R _T2=V _CE2/ I _C2... R _TN=V _CEN/ I _CNObtain: when an IGBT collector current value is I _C1-I _CNThe time the one IGBT the 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 the high order curve match in MATLAB, the on state resistance R of an IGBT when obtaining temperature and being 125 ℃ _TWith collector current I _CRelationship;

13) the first fly-wheel diode forward conduction voltage V when temperature is 125 ℃ _F-DC Forward Current I _FRelation curve in, obtain following M group data through 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 first fly-wheel diode, V _F1-V _FMBe that DC Forward Current value when first fly-wheel diode is I _F1-I _FMThe time first fly-wheel diode the 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 the high order curve match in MATLAB, the first fly-wheel diode forward conduction voltage V when obtaining temperature and being 125 ℃ _FWith DC Forward Current I _FRelationship;

According to formula: R _D1=V _F1/ I _F1, R _D2=V _F2/ I _F2... R _DM=V _CEM/ I _CMThe DC Forward Current value that obtains when first fly-wheel diode is I _F1-I _FMThe time 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 the high order curve match in MATLAB, the first fly-wheel diode on state resistance R when obtaining temperature and being 125 ℃ _DWith DC Forward Current I _FRelationship;

14) four curves in the step 11) are carried 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 alpha of the on-state loss of an IGBT and the 2nd IGBT _TJunction temperature alpha with the on-state loss of first fly-wheel diode and second fly-wheel diode _D, in the above-mentioned formula, t is the working temperature of current environment;

15) as shown in Figure 3, in curve fitting module, calculate the threshold voltage V such as real-time on-state of an IGBT through following formula _CEX, first fly-wheel diode 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 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) with V _CEXAnd R _TXThe following formula of substitution is through calculating the middle on-state loss P of an IGBT _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 the 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 _EFBe the threshold voltages such as on-state of IGBT, I _EFBe the equivalent electric current of the on-state of IGBT,

Be 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 _EFFunction for t and i;

With V _DXAnd R _DXThe following formula of substitution is through calculating the middle on-state loss P of first fly-wheel diode _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 the above formula, the upper and lower bridge arm electric current that flows into modularization multi-level converter is i, V _DFBe the threshold voltages such as on-state of fly-wheel diode, I _DFBe the equivalent electric current of the 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 _DFSFunction for 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, through step 11)-step 16) draw the threshold voltage V ' such as 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 second fly-wheel diode _DFSMiddle on-state loss P with first fly-wheel diode _DFSComputational methods identical, through step 11)-step 16) draw the threshold voltage V ' such as real-time on-state of second fly-wheel diode _DX, second fly-wheel diode real-time on-state substitutional resistance R ' _DXMiddle on-state loss P ' with second fly-wheel diode _DFS

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

19) calculate the on-state loss P of an IGBT through following formula _EF, the 2nd IGBT on-state loss P ' _EF, first fly-wheel diode on-state loss P _DFOn-state loss P ' with second fly-wheel diode _DF:

P _EF＝s1×P _EFS

P′ _EF＝s2×P′ _EFS

$P_{\mathrm{EF}}^{\′}=s2\×P_{\mathrm{EFS}}^{\′}$

P _DF＝s3×P _DFS

P′ _DF＝s4×P′ _DFS。

Step 18) specifically may further comprise the steps;

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

182) as shown in Figure 6; Duty ratio mean value is found the solution module and respectively the duty ratio of second fly-wheel diode in the duty ratio of first fly-wheel diode in the duty ratio of the 2nd IGBT in the duty ratio of an IGBT in each SM module, each SM module, each SM module and each the SM module is averaged, and output is respectively the mean value s4 of the duty ratio of second fly-wheel diode in mean value s3 and all the SM modules of the duty ratio of first fly-wheel diode among the mean value s2, all SM modules of the duty ratio of the 2nd IGBT among the mean value s1, all SM modules of the duty ratio of an IGBT 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 the turn off process; In theory can be through asking definite integral to come the switching loss of calculating device to the product of electric current and voltage; But provide the function of time of the voltage and current of switching process, very difficulty.The present invention is through 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 first fly-wheel diode and second fly-wheel diode in each SM module;

Step 2) specifically may further comprise the 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 an IGBT can bear) and the first fly-wheel diode reverse recovery loss _D(in the temperature range that first fly-wheel diode can bear) calculated both with variation of temperature, and its computing formula is following:

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

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

In the above-mentioned formula, E _Sw1Be the energy loss in the switching process of an IGBT when meeting the following conditions: an IGBT supply voltage V _CcBe reference voltage u _Ref, the rated current electric current is reference current i _Ref, junction temperature is 125 ℃; E _Sw2Be the energy loss in the switching process of an IGBT when meeting the following conditions: an IGBT supply voltage V _CcBe reference voltage u _Ref, rated current is reference current i _Ref, junction temperature is 25 ℃; E _Sw1And E _Sw2All know through the product description of an IGBT; In the reality, two IGBT of each SM module the inside adopt same model usually, so relevant parameters such as the reference voltage of the 2nd IGBT, reference current are all identical with an IGBT.

E _Rec1Be the reverse recovery energy loss of first fly-wheel diode when meeting the following conditions: voltage is reference voltage u _Ref, DC Forward Current is reference current i _Ref, junction temperature is 125 ℃; E _Rec2Be the reverse recovery energy loss of first fly-wheel diode when meeting the following conditions: voltage is reference voltage u _Ref, DC Forward Current is reference current i _Ref, junction temperature is 25 ℃; E _Rec1And E _Rec2All know through the product description of first fly-wheel diode; In each SM module, the reference voltage of first fly-wheel diode, reference current are identical with an IGBT, and the reference voltage of second fly-wheel diode, reference current 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, the switching frequency measurement module obtains the switching frequency f of an IGBT through the number of measurement unit's SM module trigger impulse in the time _STWith the switching frequency (both equate) of the 2nd IGBT, but the switching frequency of first fly-wheel diode can't directly record.Yet IGBT opens and when having electric current to flow through, first fly-wheel diode is in off state in each SM module; First fly-wheel diode is opened and when having electric current to flow through, an IGBT also is in opening state does not just have electric current to flow through, therefore, and the switching frequency f of an IGBT _STBe the first fly-wheel diode switching frequency f _SDTwice.

23) calculate the switching loss P of an IGBT through following formula _SwTReverse recovery loss P with 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 the above-mentioned formula, U _CBe 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 ℃ of working junction temperatures;

24) the switching loss P ' of the 2nd IGBT _SwTSwitching loss P with an IGBT _SwTComputational methods identical, through step 21)-step 23) obtain the switching loss P ' of the 2nd IGBT _SwT

The reverse recovery loss P ' of second fly-wheel diode _SwDReverse recovery loss P with a fly-wheel diode _SwDComputational methods identical, through step 21)-step 23) obtain the reverse recovery loss P ' of second fly-wheel diode _SwD

3) as shown in Figure 7, with IGBT module parameter (V _CE, V _d, R _t, R _d, α _T, α _D, ρ _T, ρ _D), U _c, t, i _a, i _b, i _c, the switching frequency of two IGBT and two fly-wheel diodes inputs in the loss computing module among the s1, s2, s3, s4, each SM module, calculates the total on-state loss P of IGBT through the 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 _TconBe all SM module I GBT on-state loss sums of modularization multi-level converter, the 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 _DconBe all SM module fly-wheel diode on-state loss sums of modularization multi-level converter, the fly-wheel diode on-state loss is the on-state loss P of first fly-wheel diode _DFOn-state loss P ' with second fly-wheel diode _DFSum;

IGBT master switch loss P _TswBe all SM module I GBT switching loss sums of modularization multi-level converter, the 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 _DrecBe all SM module fly-wheel diode reverse recovery loss sums of modularization multi-level converter, the fly-wheel diode reverse recovery loss is the reverse recovery loss P of first fly-wheel diode _SwDReverse recovery loss P ' with second fly-wheel diode _SwDSum;

IGBT total losses P _TBe the total on-state loss P of IGBT _TconWith IGBT master switch loss P _TswSum;

Fly-wheel diode total losses P _DBe 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 _ConBe 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 _SwBe IGBT master switch loss P _TswWith the total reverse recovery loss P of fly-wheel diode _DrecSum;

Modularization multi-level converter total losses P _TotBe IGBT total losses P _TWith fly-wheel diode total losses P _DSum;

Said modularization multi-level converter loss ratio K is the modularization multi-level converter total losses and the ratio of system's total transmission capacity.System's total transmission capacity is the set point of a modularization multi-level converter, and for a fixing modularization multi-level converter, its capacity confirms, can be through measuring.

Claims (5)

1. online loss computational methods of modularization multi-level converter is characterized in that it may further comprise the steps:

1) obtains A phase brachium pontis current i through measuring _a, B phase brachium pontis current i _b, C phase brachium pontis current i _cWith the working temperature t of current environment, calculate the on-state loss of an IGBT, the 2nd IGBT, first fly-wheel diode and second fly-wheel diode in each SM module then:

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

3) calculate the total on-state loss P of IGBT through the 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.

2. the online loss computational methods of a kind of modularization multi-level converter according to claim 1 is characterized in that said step 1) specifically may further comprise the steps:

11) from product description, obtain following four curves: the collection emitter voltage V ' of IGBT when temperature is 25 ℃ _CEWith collector current I _CRelation curve, the collection emitter voltage V of IGBT when temperature is 125 ℃ _CEWith collector current I _CRelation curve, the forward conduction voltage V ' of first fly-wheel diode when temperature is 25 ℃ _F-DC Forward Current I _FThe forward conduction voltage V of relation curve and temperature first fly-wheel diode when being 125 ℃ _F-DC Forward Current I _FRelation curve;

12) the collection emitter voltage V of an IGBT when temperature is 125 ℃ _CEWith collector current I _CRelation curve in, obtain following N group data through 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 _CENBe an IGBT collector current value to be I _C1-I _CNThe time 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 the high order curve match in MATLAB, an IGBT collection emitter voltage V when obtaining temperature and being 125 ℃ _CEWith collector current I _CRelationship;

According to formula: R _T1=V _CE1/ I _C1, R _T2=V _CE2/ I _C2... R _TN=V _CEN/ I _CNObtain: when an IGBT collector current value is I _C1-I _CNThe time the one IGBT the 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 the high order curve match in MATLAB, the on state resistance R of an IGBT when obtaining temperature and being 125 ℃ _TWith collector current I _CRelationship;

13) the first fly-wheel diode forward conduction voltage V when temperature is 125 ℃ _F-DC Forward Current I _FRelation curve in, obtain following M group data through 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 first fly-wheel diode, V _F1-V _FMBe that DC Forward Current value when first fly-wheel diode is I _F1-I _FMThe time first fly-wheel diode the 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 the high order curve match in MATLAB, the first fly-wheel diode forward conduction voltage V when obtaining temperature and being 125 ℃ _FWith DC Forward Current I _FRelationship;

According to formula: R _D1=V _F1/ I _F1, R _D2=V _F2/ I _F2... R _DM=V _CEM/ I _CMThe DC Forward Current value that obtains when first fly-wheel diode is I _F1-I _FMThe time 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 the high order curve match in MATLAB, the first fly-wheel diode on state resistance R when obtaining temperature and being 125 ℃ _DWith DC Forward Current I _FRelationship;

14) four curves in the step 11) are carried 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 alpha of the on-state loss of an IGBT and the 2nd IGBT _TJunction temperature alpha with the on-state loss of first fly-wheel diode and second fly-wheel diode _D, in the above-mentioned formula, t is the working temperature of current environment;

15) in curve fitting module, calculate the threshold voltage V such as real-time on-state of an IGBT through following formula _CEX, first fly-wheel diode 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 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) with V _CEXAnd R _TXThe following formula of substitution is through calculating the middle on-state loss P of an IGBT _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 the 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 _EFBe the threshold voltages such as on-state of IGBT, I _EFBe the equivalent electric current of the on-state of IGBT,

Be 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 _EFFunction for t and i;

With V _DXAnd R _DXThe following formula of substitution is through calculating the middle on-state loss P of first fly-wheel diode _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 the above formula, the upper and lower bridge arm electric current that flows into modularization multi-level converter is i, V _DFBe the threshold voltages such as on-state of fly-wheel diode, I _DFBe the equivalent electric current of the 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 _DFSFunction for 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, through step 11)-step 16) draw the threshold voltage V ' such as 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 second fly-wheel diode _DFSMiddle on-state loss P with first fly-wheel diode _DFSComputational methods identical, through step 11)-step 16) draw the threshold voltage V ' such as real-time on-state of second fly-wheel diode _DX, second fly-wheel diode real-time on-state substitutional resistance R ' _DXMiddle on-state loss P ' with second fly-wheel diode _DFS

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

19) calculate the on-state loss P of an IGBT through following formula _EF, the 2nd IGBT on-state loss P ' _EF, first fly-wheel diode on-state loss P _DFOn-state loss P ' with 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。

3. the online loss computational methods of a kind of modularization multi-level converter according to claim 2 is characterized in that said step 18) specifically may further comprise the steps;

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

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

4. the online loss computational methods of a kind of modularization multi-level converter according to claim 1 is characterized in that said step 2) specifically may further comprise the 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 with variation of temperature, its computing formula is following:

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

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

In the above-mentioned formula, E _Sw1Be the energy loss in the switching process of an IGBT when meeting the following conditions: an IGBT supply voltage V _CcBe reference voltage u _Ref, the rated current electric current is reference current i _Ref, junction temperature is 125 ℃; E _Sw2Be the energy loss in the switching process of an IGBT when meeting the following conditions: an IGBT supply voltage V _CcBe reference voltage u _Ref, rated current is reference current i _Ref, junction temperature is 25 ℃; E _Sw1And E _Sw2All know through the product description of an IGBT;

E _Rec1Be the reverse recovery energy loss of first fly-wheel diode when meeting the following conditions: voltage is reference voltage u _Ref, DC Forward Current is reference current i _Ref, junction temperature is 125 ℃; E _Rec2Be the reverse recovery energy loss of first fly-wheel diode when meeting the following conditions: voltage is reference voltage u _Ref, DC Forward Current is reference current i _Ref, junction temperature is 25 ℃; E _Rec1And E _Rec2All know through the product description of first fly-wheel diode;

22) the switching frequency measurement module obtains the switching frequency f of an IGBT through the number of measurement unit's SM module trigger impulse in the time _ST, the switching frequency f of first fly-wheel diode _SDBe the switching frequency f of an IGBT _STHalf the;

23) calculate the switching loss P of an IGBT through following formula _SwTReverse recovery loss P with 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 the above-mentioned formula, U _CBe 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 first fly-wheel diode under the maximum junction temperature;

24) the switching loss P ' of the 2nd IGBT _SwTSwitching loss P with an IGBT _SwTComputational methods identical, through step 21)-step 23) obtain the switching loss P ' of the 2nd IGBT _SwT

The reverse recovery loss P ' of second fly-wheel diode _SwDReverse recovery loss P with a fly-wheel diode _SwDComputational methods identical, through step 21)-step 23) obtain the reverse recovery loss P ' of second fly-wheel diode _SwD

5. the online loss computational methods of a kind of modularization multi-level converter according to claim 1 is characterized in that, the total on-state loss P of said IGBT _TconBe all SM module I GBT on-state loss sums of modularization multi-level converter, the 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 said fly-wheel diode _DconBe all SM module fly-wheel diode on-state loss sums of modularization multi-level converter, the fly-wheel diode on-state loss is the on-state loss P of first fly-wheel diode _DFOn-state loss P ' with second fly-wheel diode _DFSum;

Said IGBT master switch loss P _TswBe all SM module I GBT switching loss sums of modularization multi-level converter, the 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 said fly-wheel diode _DrecBe all SM module fly-wheel diode reverse recovery loss sums of modularization multi-level converter, the fly-wheel diode reverse recovery loss is the reverse recovery loss P of first fly-wheel diode _SwDReverse recovery loss P ' with second fly-wheel diode _SwDSum;

Said IGBT total losses P _TBe the total on-state loss P of IGBT _TconWith IGBT master switch loss P _TswSum;

Said fly-wheel diode total losses P _DBe 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 said modularization multi-level converter _ConBe the total on-state loss P of IGBT _TconWith the total on-state loss P of fly-wheel diode _DconSum;

Said modularization multi-level converter master switch loss P _SwBe IGBT master switch loss P _TswWith the total reverse recovery loss P of fly-wheel diode _DrecSum;

Said modularization multi-level converter total losses P _TotBe IGBT total losses P _TWith fly-wheel diode total losses P _DSum;

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

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