CN105811771A - Method for determining loss of MMC isolation type DC/DC converter switch - Google Patents

Abstract

The invention relates to a method for determining loss of an MMC isolation type DC/DC converter switch. The method comprises that parameter fitting for a switch loss characteristic curve of an MMC neutron module power device is carried out; the switch loss energy of a sub module power device at the operation junction temperature is calculated by utilizing an interpolation method; the average switch loss of a single power device is determined; switch loss type distribution of an MMC-DC/AC/DC converter in an AC period is determined; the average switch loss of single-phase upper and lower arms of an input end MMC converter is determined; the switch loss of all power devices of the MMC-DC/AC/DC converter is determined. According to the switch loss equivalent displacement method, an analysis expression for isolation type DC/DC converter switch loss based on a modular multilevel converter is effectively solved, and the MMC-DC/DC converter switch loss value calculation method is disclosed. Quantitative analysis on isolation type MMC-DC/DC converter switch loss is facilitated, and system parameter optimization design programs are conveniently realized and integrated.

Description

A kind of defining method based on MMC isolated form DC/DC converter switches loss

Technical field

The present invention relates to the defining method of a kind of switching loss, be specifically related to a kind of defining method based on MMC isolated form DC/DC converter switches loss.

Background technology

The shortage of traditional energy and going from bad to worse of environment, greatly promoted the development and utilization of the clean energy resourcies such as green regenerative energy sources.But being limited to the digestion capability of local power system, major part regenerative resource is not utilized effectively, and " abandoning wind ", " abandoning light " phenomenon even occurs, it is badly in need of carrying out that wind, photoelectromotive force be extensive, high efficiency, safety send research outside.Direct current network technology based on customary DC and flexible direct current is one of effective technology means solving this present situation.And hindering one of principal element that direct current network formed is the disappearance of high-voltage large-capacity DC/DC changer so that the DC power transmission line that each electric pressure is different can not be joined directly together and form large-scale DC transmission system.At present, the research of DC/DC changer technology is concentrated mainly on middle low power mesolow electric pressure, and along with constantly building and direct current network demand day by day urgent of DC line, high-voltage large-capacity DC/DC changer technology is urgently to be resolved hurrily.

Based on modularization multi-level converter (ModularMultilevelConverter, MMC) isolated form high-voltage large-capacity DC/DC changer becomes study hotspot due to its plurality of advantages, this topology is connected to form through isolating transformer by two MMC inverters, such as Fig. 1 depicted.The MMC converter bridge arm of input and output side all adopts the mode that submodule is connected, as in figure 2 it is shown, effectively alleviate driving concordance that under high pressure occasion, a large amount of power devices are directly connected encountered and equal hard requirement such as pressure.This DC/DC convertor controls is flexible, it is not necessary to the change of hardware circuit and control strategy can realize the two-way flow of energy.Input and output side carries out electrical isolation by isolating transformer, effectively prevents spreading of the system failure.Isolating transformer can be operated in 500Hz to 1kHz, rising along with operating frequency, in changer, the passive device such as electric capacity, inductance volume reduces, but the loss of IGBT constant power device rises, therefore in optimization design is compromised in system loss and volume, the loss further investigation of MMC-DC/AC/DC changer is essential.

The loss of power device is made up of on-state loss and switching loss, and the appraisal procedure of its loss can be divided into testing inspection, physical modeling and mathematical analysis three class.Method for testing and detecting is only applicable to low pressure small-power occasion, and the method for physical modeling will based on substantial amounts of device Fabrication parameter, it is difficult to obtain.Current MMC inverter Loss Research all adopts mathematical methods, according to some component characteristic parameters that manufacturer provides, the characterisitic function of fitting power device, and then carry out the loss evaluation based on power device average current and effective current or online loss calculation, all cannot be simply obtained the quantitative relationship of MMC switching loss and voltage modulated degree, brachium pontis submodule quantity, transformator operating frequency and meritorious through-put power etc., be not easy to carry out quantitative analysis and the Optimized System Design of switching loss.

Summary of the invention

For solving above-mentioned deficiency of the prior art, it is an object of the invention to provide the defining method based on MMC isolated form DC/DC converter switches loss, the present invention adopts the method for switching loss equivalent replacement, effectively solve the analytical expression of the isolated form DC/DC converter switches loss based on modularization multi-level converter, disclose the numerical computation method of a kind of MMC-DC/DC converter switches loss.Contribute to the quantitative analysis of MMC-DC/DC converter switches loss, it is simple to the realization of systematic parameter Optimized Program is with integrated.

It is an object of the invention to adopt following technical proposals to realize:

The present invention provides a kind of defining method based on MMC isolated form DC/DC converter switches loss, described isolated form DC/DC changer to include isolating transformer and the MMC of two ends connection thereof；Two MMC all access in straight-flow system；Modularization multi-level converter MMC is made up of three-phase, is often made up of upper and lower two brachium pontis that the structure connected is identical；The exchange end of the midpoint connection mode massing multilevel converter of upper and lower two brachium pontis；

In described upper and lower two brachium pontis, each brachium pontis includes 1 reactor submodule identical with N number of structure；After the sub module cascade of each brachium pontis, one end is connected with the exchange end of modularization multi-level converter by reactor；After the sub module cascade of each brachium pontis, the other end is connected with submodule one end of the cascade of two other phase brachium pontis, forms the both positive and negative polarity bus of modular multilevel voltage source converter DC terminal；Described submodule is made up of the capacitor branches that half-bridge is connected in parallel, and described half-bridge is made up of upper brachium pontis and lower brachium pontis, and described upper brachium pontis and lower brachium pontis form by insulated gate bipolar transistor IGBT and fly-wheel diode FWD connected in parallel；

It thes improvement is that, described method comprises the steps:

Step 1: the switching loss characteristics of MMC Neutron module power device is carried out parameter fitting；

Step 2: utilize the switching loss energy of submodule power device under interpolation calculation working junction temperature；

Step 3: determine the average switch loss of single power device；

Step 4: determine the distribution of switching loss type in MMC-DC/AC/DC changer ac cycle；

Step 5: determine the average switch loss of the single-phase upper and lower brachium pontis of input MMC inverter；

Step 6: determine the switching loss of all power devices of MMC-DC/AC/DC changer.

Further, in described step 1, for the power device switching loss characteristics in submodule, adopt the quadratic polynomial such as following formula (1) to intend united extraction switching loss characterisitic parameter, ask for the energy loss of once switch motion on given on state current:

Wherein: E_{sw_k}Represent junction temperature be k DEG C at the opening of IGBT, turn off or the reverse recovery loss (E of diode_on, E_offOr E_rec)；i_devRepresent the electric current flowing through power device, be collector current i for IGBT_C, it is forward current i for diode_F；a_{sw_k}、b_{sw_k}、c_{sw_k}It is the parameter determined by 25 DEG C and 125 DEG C of energy consumption curve matchings respectively, is fitted obtaining a to IGBT turn-on consumption curve_{on_k}、b_{on_k}、c_{on_k}, it is fitted obtaining a to IGBT turn-off power loss curve_{off_k}、b_{off_k}、c_{off_k}, it is fitted obtaining a to diode reverse recovery losses curve_{rec_k}、b_{rec_k}、c_{rec_k}。

Further, in described step 2, according to the energy consumption curve fitting result of power device in 25 DEG C and 125 DEG C of submodules, utilize interpolation calculation working junction temperature T_jThe switching loss energy of power device in submodule at DEG C, as shown in following formula (2)；Bring formula (1) into formula (2) and carry out abbreviation, obtain formula (3)-(6):

$E_{\mathrm{swTj}}=(E_{\mathrm{sw}\_125}-E_{\mathrm{sw}\_25})\·\frac{T_j-25}{100}+E_{\mathrm{sw}\_25}---\left(2\right);$

$E_{\mathrm{swTj}}=a_{\mathrm{swTj}}+b_{\mathrm{swTj}}\·i_{\mathrm{dev}}+c_{\mathrm{swTj}}\·i_{\mathrm{dev}}^2---\left(3\right);$

$a_{\mathrm{swTj}}=(a_{\mathrm{sw}\_125}-a_{\mathrm{sw}\_25})\·\frac{T_j-25}{100}+a_{\mathrm{sw}\_25}---\left(4\right);$

$b_{\mathrm{swTj}}=(b_{\mathrm{sw}\_125}-b_{\mathrm{sw}\_25})\·\frac{T_j-25}{100}+b_{\mathrm{sw}\_25}---\left(5\right);$

$c_{\mathrm{swTj}}=(c_{\mathrm{sw}\_125}-c_{\mathrm{sw}\_25})\·\frac{T_j-25}{100}+c_{\mathrm{sw}\_25}---\left(6\right);$

Wherein: E_swTjRepresent junction temperature be Tj DEG C at the switching loss energy of power device in submodule；a_swTj、b_swTj、c_swTjRespectively junction temperature be Tj DEG C at the parameter in the switching loss expression formula of power device in submodule；E_{sw_125}Represent that junction temperature is the opening of IGBT at 125 DEG C, turns off or the reverse recovery loss of diode；E_{sw_25}Represent that junction temperature is the opening of IGBT at 25 DEG C, turns off or the reverse recovery loss of diode；a_{sw_125}、b_{sw_125}、c_{sw_125}Represent the parameter determined by 125 DEG C of energy consumption curve matchings, be fitted obtaining a to IGBT turn-on consumption curve_{on_125、}b_{on_125}、c_{on_125}, it is fitted obtaining a to IGBT turn-off power loss curve_{off_125}、b_{off_125}、c_{off_125}, it is fitted obtaining a to diode reverse recovery losses curve_{rec_125}、b_{rec_125}、c_{rec_125}；a_{sw_25}、b_{sw_25}、c_{sw_25}Represent the parameter determined by 25 DEG C of energy consumption curve matchings, be fitted obtaining a to IGBT turn-on consumption curve_{on_25}、b_{pn_25}、c_{on_25}, it is fitted obtaining a to IGBT turn-off power loss curve_{off_25}、b_{off_2}5、c_{off_25}, it is fitted obtaining a to diode reverse recovery losses curve_{rec_25}、b_{rec_25}、c_{rec_25}。

Further, in described step 3, according to the number of times turned on and off of power device in submodule, corresponding switching loss energy is added up, it is carried out time average, the average switch loss of each several part can be obtained；The turn-on consumption P of IGBTT1 in submodule_T1onWith turn-off power loss P_T1offAnd the reverse blocking loss P of diode D1_D1recComputing formula as follows:

$P_{T1\mathrm{on}}=\frac{1}{T_s}\·{\mathrm{\Σ}}_{u=1}^w\left(\frac{u_{\mathrm{dc}}}{v_{\mathrm{ceref}}}{E}_{\mathrm{onTju}}\right)---\left(7\right);$

$P_{T1\mathrm{off}}=\frac{1}{T_s}\·{\mathrm{\Σ}}_{u=1}^w\left(\frac{u_{\mathrm{dc}}}{v_{\mathrm{ceref}}}{E}_{\mathrm{offTju}}\right)---\left(8\right);$

$P_{D1\mathrm{rec}}=\frac{1}{T_s}\·{\mathrm{\Σ}}_{u=1}^w\left(\frac{u_{\mathrm{dc}}}{v_{\mathrm{ceref}}}{E}_{\mathrm{recTju}}\right)---\left(9\right);$

Wherein: u_dcFor submodule capacitor voltage；v_cerefFor the reference voltage base value in order to calculate switching loss that producer provides；E_onTjuFor IGBTT1 at working junction temperature T_jThe loss of energy of generation is opened for the u time at DEG C；E_offTjuFor IGBTT1 at working junction temperature T_jThe loss of energy produced is turned off the u time at DEG C；E_recTjuFor D1 at working junction temperature T_jThe loss of energy of the u time reverse blocking generation at DEG C；T_sFor the MMC-DC/AC/DC changer AC working cycle；W is T_sThe number of times of switch in cycle time.

Further, described step 4 comprises the steps:

Step 4.1: determine that single half-bridge submodule produces the condition of different switching loss type:

For the half-bridge sub modular structure in Fig. 2, the switching change over order of bridge arm current direction and submodule all affects switching loss type；When bridge arm current direction is just, submodule has input state to become producing the turn-on consumption of IGBTT2 and the reverse blocking loss of diode D1 in excision state procedure；

Step 4.2: determine MMC inverter upper and lower brachium pontis breaker in middle loss type:

According to MMC-DC/AC/DC changer operation mechanism, shown in the expression formula of upper and lower bridge arm voltage and electric current such as formula (10)-(13)；When brachium pontis output voltage rises, part brachium pontis submodule is input state by excising State Transferring, produces corresponding switching loss according to bridge arm current direction；When brachium pontis output voltage declines, part brachium pontis submodule is input state by excising State Transferring:

$U_{\mathrm{up}}=\frac{U_d}{2}-U_m\cos \mathrm{\θ}=\frac{U_d}{2}(1-m\·\cos \mathrm{\θ})---\left(10\right);$

$U_{\mathrm{down}}=\frac{U_d}{2}+U_m\cos \mathrm{\θ}=\frac{U_d}{2}(1+m\·\cos \mathrm{\θ})---\left(11\right)$

Wherein: U_upFor upper brachium pontis output voltage；U_downFor lower brachium pontis output voltage；U_dFor DC voltage；U_mFor MMC-DC/AC/DC changer AC output voltage peak value；θ is the phase angle of alternating voltage；M is voltage modulated degree；i_upFor upper bridge arm current, I_dFor MMC Converter DC-side electric current；I_mFor ac-side current peak value；Phase angle difference for AC voltage Yu electric current；K is current-modulation degree.

Further, described step 5 comprises the steps:

Step 5.1: switching loss is carried out equivalent replacement so that the switchtype that upper and lower brachium pontis produces at synchronization is consistent；

Analyze through step 4.2 and show that the switching loss type that the upper and lower brachium pontis of synchronization produces is not necessarily identical, cause that system switching loss calculation solves complexity.Under the premise that guarantee system main switch loss is constant, by the equivalent replacement of switching loss so that the switchtype that upper and lower brachium pontis produces at synchronization is consistent, greatly simplify computing.

Step 5.2: calculate the average switch loss of the single-phase upper and lower brachium pontis of input MMC inverter:

Solve the switching loss in the primitive period, as shown in following formula (14):

$\begin{array}{c}{P}_{\mathrm{sw}\_1}=\frac{U_{\mathrm{cap}}}{T_s\·U_{\mathrm{ref}}}\left\{{\mathrm{\Σ}}_{h=1}^{N_1}\right[a_{\mathrm{offTj}}+b_{\mathrm{offTj}}(i_{\mathrm{uph}}+i_{\mathrm{downh}})+c_{\mathrm{offTj}}(i_{\mathrm{uph}}^2+i_{\mathrm{downh}}^2)]+\\ {\mathrm{\Σ}}_{i=1}^{N_2}[a_{\mathrm{onrecTj}}+b_{\mathrm{onrecTj}}\·(i_{\mathrm{upi}}+i_{\mathrm{downi}})+c_{\mathrm{onrecTj}}\·(i_{\mathrm{upi}}^2+i_{\mathrm{downi}}^2)]+{\mathrm{\Σ}}_{j=1}^{N_3}[a_{\mathrm{offTj}}+\\ b_{\mathrm{offTj}}(i_{\mathrm{upj}}+i_{\mathrm{downj}})+c_{\mathrm{offTj}}(i_{\mathrm{upj}}^2+i_{\mathrm{downj}}^2)]+{\mathrm{\Σ}}_{k=1}^{N4}[a_{\mathrm{onrecTj}}+b_{\mathrm{onrecTj}}\·(i_{\mathrm{upk}}+\\ i_{\mathrm{downk}})+c_{\mathrm{onrecTj}}\·(i_{\mathrm{upk}}^2+i_{\mathrm{downk}}^2)\left]\right\}\end{array}---\left(14\right);$

a_onrecTj=a_onTj+a_recTj(15)；

b_onrecTj=b_onTj+b_recTj(16)；

c_onrecTj=c_onTj+c_recTj(17)；

Wherein: P_{sw_1}For the switching loss of power device in the single-phase upper and lower brachium pontis of MMC inverter；N1 represent [0, pi/2) interior brachium pontis submodule switching conversion number of times；N2 represent [pi/2, π) interior brachium pontis submodule switching conversion number of times；N3 represent [π, 3 pi/2s) interior brachium pontis submodule switching conversion number of times；N4 represent [3 pi/2s, 2 π) interior brachium pontis submodule switching conversion number of times；i_uphAnd i_downhFor [0, pi/2) conversion of the h time switching of interior brachium pontis time corresponding upper bridge arm current and lower bridge arm current；i_upiAnd i_downiFor [pi/2, π) conversion of interior brachium pontis i & lt switching time corresponding upper bridge arm current and lower bridge arm current；i_upjAnd i_downjFor [π, 3 pi/2s) conversion of interior brachium pontis jth time switching time corresponding upper bridge arm current and lower bridge arm current；i_upkAnd i_downkFor [3 pi/2s, 2 π) conversion of interior brachium pontis kth time switching time corresponding upper bridge arm current and lower bridge arm current；U_capFor submodule electric capacity rated voltage；a_onrecTj、b_onrecTj、c_onrecTjRepresent the sum of IGBT turn-on consumption curve and diode reverse cut-off loss curve fitting parameter under Tj junction temperature respectively；Ts is the MMC-DC/AC/DC changer AC working cycle；

Step 5.3: bring upper and lower bridge arm current expression formula (12) and (13) into formula (14) and simplify:

$\begin{array}{c}{P}_{\mathrm{sw}\_1}=\frac{U_{\mathrm{cap}}}{T_s\·U_{\mathrm{ref}}}[N_1(a_{\mathrm{offTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{offTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{offTj}})+{\mathrm{\Σ}}_{h=1}^{N_1}{c}_{\mathrm{offTj}}\frac{1}{2}{I}_m^2{\cos }^2{\mathrm{\θ}}_{1h}+\\ N_2(a_{\mathrm{onrecTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{onrecTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{onrecTj}})+{\mathrm{\Σ}}_{i=1}^{N_2}{c}_{\mathrm{onrecTj}}\frac{1}{2}{I}_m^2{\cos }^2{\mathrm{\θ}}_{2i}+\\ N_3(a_{\mathrm{offTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{offTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{offTj}})+{\mathrm{\Σ}}_{j=1}^{N_3}{c}_{\mathrm{offTj}}\frac{1}{2}{I}_m^2{\cos }^2{\mathrm{\θ}}_{3j}+N_4(a_{\mathrm{onrecTj}}+\frac{2}{3}{i}_d\·\\ b_{\mathrm{onrecTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{onrecTj}})+{\mathrm{\Σ}}_{k=1}^{N_4}{c}_{\mathrm{onrecTj}}\frac{1}{2}{I}_m^2{\cos }^2{\mathrm{\θ}}_{4k}]\end{array}---\left(18\right);$

Step 5.4: utilize the quantitative relationship that modulation strategy is corresponding to simplify average switch loss:

Assuming that in half-bridge submodule, upper and lower brachium pontis Neutron module number is n, is approached modulation strategy by nearest level and obtains, upper and lower brachium pontis reference voltage compares with threshold voltage value, generates and modulates signal accordingly；Threshold voltage is respectively as follows: 0,N+1 altogether, θ_1hRepresent bridge arm voltage modulating wave (0, pi/2] in the h time angle corresponding with threshold voltage intersection；θ_2iRepresent bridge arm voltage modulating wave (pi/2, π] the interior i & lt angle corresponding with threshold voltage intersection；θ_3jRepresent bridge arm voltage modulating wave [π, 3 pi/2s) time corresponding with the threshold voltage intersection angle of interior jth；θ_4kRepresent bridge arm voltage modulating wave [3 pi/2s, 2 π) time corresponding with the threshold voltage intersection angle of interior kth；Obtain analytical expression (19)-(22), and formula (19)-(22) are brought into formula (18) relational expression (24), obtain formula (25) through ordered series of numbers summation:

$\frac{U_d}{2}-U_m\cos {\mathrm{\θ}}_{1h}=\left(\right[\frac{n\·(1-m)}{2}]+h-1)\·\frac{U_d}{n};h=\mathrm{1,2},...N_1---\left(19\right);$

$\frac{U_d}{2}-U_m\cos {\mathrm{\θ}}_{2i}=(\frac{n}{2}+h-1)\·\frac{U_d}{n};i=\mathrm{1,2}...N_2---\left(20\right);$

$\frac{U_d}{2}-U_m\cos {\mathrm{\θ}}_{3j}=(n-[\frac{n\·(1-m)}{2}]-h-1)\·\frac{U_d}{n};j=\mathrm{1,2},...N_3---\left(21\right);$

$\frac{U_d}{2}-U_m\cos {\mathrm{\θ}}_{4k}=(\frac{n}{2}-h-1)\·\frac{U_d}{n};k=\mathrm{1,2}...N_4---\left(22\right);$

$N_1=N_2=N_3=N_4=(\frac{n}{2}-[\frac{n\·(1-m)}{2}\left]\right)=\frac{n}{2}-Q---\left(23\right);$

$\begin{array}{c}{P}_{\mathrm{sw}\_1}=\frac{U_{\mathrm{cap}}}{T_s\·U_{\mathrm{ref}}}\{N_1(a_{\mathrm{offTj}}+\frac{2}{3}{i}_d\·d_{\mathrm{offTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{offTj}})+\frac{c_{\mathrm{offTj}}}{2}\·I_m^2\·{\left(\frac{U_d}{U_m}\right)}^2\·[{(\frac{1}{2}-\frac{Q}{n})}^2+\\ {(\frac{1}{2}-\frac{Q+1}{n})}^2+...+{(\frac{1}{2}-\frac{\frac{n}{2}-1}{2})}^2]+N_2(a_{\mathrm{onrecTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{onrecTj}}+\frac{2}{9}\·c_{\mathrm{onrecTj}})+\\ \frac{c_{\mathrm{onrecTj}}}{2}\·I_m^2\·{\left(\frac{U_d}{U_m}\right)}^2\·[{\left(\frac{1}{n}\right)}^2+{\left(\frac{2}{n}\right)}^2+...+{(\frac{1}{2}-\frac{Q}{n})}^2]+N_3(a_{\mathrm{offTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{offTj}}+\frac{2}{9}\·i_d^2\·\\ c_{\mathrm{offTj}})+\frac{c_{\mathrm{offTj}}}{2}\·I_m^2\·{\left(\frac{U_d}{U_m}\right)}^2\·{[\left(\frac{1}{n}\right)}^2+{\left(\frac{2}{n}\right)}^2+...+{(\frac{1}{2}-\frac{Q}{n})}^2]+N_4(a_{\mathrm{onrecTj}}+\frac{2}{3}{i}_d\·)\\ b_{\mathrm{onrecTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{onrecTj}})+\frac{c_{\mathrm{onrecTj}}}{2}\·I_m^2\·{\left(\frac{U_d}{U_m}\right)}^2\·[{\left(\frac{1}{n}\right)}^2+{\left(\frac{2}{n}\right)}^2+...+{(\frac{1}{2}-\frac{Q}{n})}^2]\}\end{array}---\left(24\right);$

$\begin{array}{c}{P}_{\mathrm{sw}\_1}=\frac{U_{\mathrm{cap}}}{T_s\·U_{\mathrm{ref}}}\{(n-2Q)\·(a_{\mathrm{onoffrecTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{onoffrecTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{onoffrecTj}})+\\ c_{\mathrm{onoffrecTj}}\·I_m^2\·{\left(\frac{1}{m}\right)}^2\·\frac{1}{12n^2}(n-2Q)(n-2Q+1)\·(n-2Q+2)\}\end{array}---\left(25\right);$

a_onoffrecTj=a_onTj+a_offTj+a_recTj(26)；

b_onoffrecTj=b_onTj+b_offTj+b_recTj(27)；

c_onoffecTj=c_onTj+c_offTj+c_recTj(28)；

Wherein: [], for rounding algorithm, Q represents bracket function, the different voltage modulated degree impact on loss of reaction；H represent (0, pi/2] in the number of times that intersects with threshold voltage of bridge arm voltage modulating wave；a_onoffrecTj、b_onoffrecTj、c_onoffrecTjRepresent the sum of IGBT turn-on consumption, turn-off power loss and diode reverse cut-off loss curve fitting parameter when junction temperature is Tj respectively.

Further, described step 6 comprises the steps:

Step 6.1: calculate the switching loss of input MMC inverter three phase power device；

MMC inverter symmetrical operation, solves the switching loss of input MMC inverter three phase power device, as shown in following formula (29) according to step 5:

P_{sw_3}=3*P_{sw_1}(29)；

Step 6.2: calculate the switching loss of outfan MMC inverter three phase power device: as shown in following formula (30):

P′_{sw_3}=3*P '_{sw_1}(30)；

Step 6.2: calculate the switching loss of all power devices in MMC-DC/AC/DC changer

The switching loss of input and outfan MMC in step 6.1 and 6.2 is added to obtain the switching loss of all power devices in MMC-DC/AC/DC changer, as shown in following formula (31):

P_total=P_{sw_3}+P′_{sw_3}(31)；

Wherein: P_totalSwitching loss for power devices all in MMC-DC/AC/DC changer.

Compared with immediate prior art, the excellent effect that technical scheme provided by the invention has is:

1, MMC-DC/AC/DC converter switches loss computing method provided by the present invention turns on and off moment based on each power device is each, adopts the method for loss equivalent replacement to push over, explicit physical meaning；

2, MMC-DC/AC/DC converter switches loss computing method provided by the present invention can calculate and obtain the analytical expression of each power device switching loss in changer, turn on and off on-state loss and diode reverse including IGBT block loss, it is possible to realize the relative analysis between each loss；

3, MMC-DC/AC/DC converter switches loss calculation expression formula provided by the present invention can obtain the quantitative relationship of converter switches loss and voltage modulated degree, brachium pontis submodule quantity, transformator operating frequency, merit through-put power, it is simple to systematic parameter optimization design and loss braking measure research.

Accompanying drawing explanation

Fig. 1 is based on the isolated form DC/DC converter topology figure of MMC；

Fig. 2 is modularization multi-level converter circuit topology figure provided by the invention；

Fig. 3 is the IGBT provided by the invention performance diagram turning on and off loss；

Fig. 4 is the performance diagram that diode reverse provided by the invention blocks；

Fig. 5 is MMC converter bridge arm current waveform figure provided by the invention, and wherein: dotted line is upper bridge arm current oscillogram, solid line is lower bridge arm current oscillogram；

Fig. 6 is MMC converter bridge arm voltage oscillogram provided by the invention；Wherein: dotted line is upper bridge arm voltage oscillogram, solid line is lower bridge arm voltage oscillogram；

Fig. 7 is MMC inverter loss scattergram after equivalent replacement provided by the invention；Wherein: dotted line is upper brachium pontis loss figure, solid line is lower brachium pontis loss figure；

Fig. 8 is that nearest level provided by the invention approaches the quantitative relationship figure that modulation strategy is corresponding；

Fig. 9 is the flow chart of the defining method based on MMC isolated form DC/DC converter switches loss provided by the invention.

Detailed description of the invention

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

The present invention provides the computational methods of a kind of isolated form DC/DC converter switches loss based on modularization multi-level converter MMC, wherein: isolated form DC/DC changer includes isolating transformer and the MMC of two ends connection thereof；Two MMC all access in straight-flow system；Modularization multi-level converter MMC is made up of three-phase, is often made up of upper and lower two brachium pontis that the structure connected is identical；The exchange end of the midpoint connection mode massing multilevel converter of upper and lower two brachium pontis；

In described upper and lower two brachium pontis, each brachium pontis includes 1 reactor submodule identical with N number of structure；After the sub module cascade of each brachium pontis, one end is connected with the exchange end of modularization multi-level converter by reactor；After the sub module cascade of each brachium pontis, the other end is connected with submodule one end of the cascade of two other phase brachium pontis, forms the both positive and negative polarity bus of modular multilevel voltage source converter DC terminal；Described submodule is made up of the capacitor branches that half-bridge is connected in parallel, and described half-bridge is made up of upper brachium pontis and lower brachium pontis, and described upper brachium pontis and lower brachium pontis form by insulated gate bipolar transistor IGBT and fly-wheel diode FWD connected in parallel；The flow chart of computational methods is as it is shown in figure 9, comprise the steps:

Step 1: carry out parameter fitting according to the switching loss characteristics of power device:

For power device (IGBT and the diode) switching loss characteristics that producer provides, the quadratic polynomial such as formula (1) is adopted to intend united extraction switching loss characterisitic parameter, thus asking for the energy loss of once switch motion on given on state current.Switching loss characteristics is referred to Fig. 3 and Fig. 4.

Wherein: E_{sw_k}Represent junction temperature be k DEG C at the opening of IGBT, turn off or the reverse recovery loss energy (E of diode_on, E_offOr E_rec)；i_devRepresent the electric current flowing through power device, be collector current i for IGBT_C, it is forward current i for diode_F)。a_{sw_k}、b_{sw_k}、c_{sw_k}It is the parameter determined by 25 DEG C and 125 DEG C of energy consumption curve matchings, is fitted obtaining a to IGBT turn-on consumption curve_{on_25}、b_{on_25}、c_{on_25}, it is fitted obtaining a to IGBT turn-off power loss curve_{off_25}、b_{off_25}、c_{off_25}, it is fitted obtaining a to diode reverse recovery losses curve_{rec_25}、b_{rec_25}、c_{rec_25}。

Step 2: utilize switching loss energy under interpolation calculation working junction temperature

According to 25 DEG C and 125 DEG C of energy consumption curve fitting results, utilize switching loss energy at interpolation calculation working junction temperature Tj DEG C, as shown in formula (2).Bring formula (1) into formula (2) and carry out abbreviation, obtain formula (3)-(6).

$E_{\mathrm{swTj}}=(E_{\mathrm{sw}\_125}-E_{\mathrm{sw}\_25})\·\frac{T_j-25}{100}+E_{\mathrm{sw}\_25}---\left(2\right);$

$E_{\mathrm{swTj}}=a_{\mathrm{swTj}}+b_{\mathrm{swTj}}\·i_{\mathrm{dev}}+c_{\mathrm{swTj}}\·i_{\mathrm{dev}}^2---\left(3\right);$

$a_{\mathrm{swTj}}=(a_{\mathrm{sw}\_125}-a_{\mathrm{sw}\_25})\·\frac{T_j-25}{100}+a_{\mathrm{sw}\_25}---\left(4\right);$

$b_{\mathrm{swTj}}=(b_{\mathrm{sw}\_125}-b_{\mathrm{sw}\_25})\·\frac{T_j-25}{100}+b_{\mathrm{sw}\_25}---\left(5\right);$

$c_{\mathrm{swTj}}=(c_{\mathrm{sw}\_125}-c_{\mathrm{sw}\_25})\·\frac{T_j-25}{100}+c_{\mathrm{sw}\_25}---\left(6\right);$

Wherein: E_swTjRepresent junction temperature be Tj DEG C at the switching loss energy of power device；a_swTj、b_swTj、c_swTjParameter in the switching loss expression formula of power device at being Tj DEG C for junction temperature；E_{sw_125}Represent that junction temperature is the opening of IGBT at 125 DEG C, turns off or the reverse recovery loss of diode；E_{sw_25}Represent that junction temperature is the opening of IGBT at 25 DEG C, turns off or the reverse recovery loss of diode；a_{sw_125}、b_{sw_125}、c_{sw_125}Represent the parameter determined by 125 DEG C of energy consumption curve matchings, be fitted obtaining a to IGBT turn-on consumption curve_{on_125}、b_{on_125}、c_{on_125}, it is fitted obtaining a to IGBT turn-off power loss curve_{off_125}、b_{off_125}、c_{off_125}, it is fitted obtaining a to diode reverse recovery losses curve_{rec_125}、b_{rec_125}、c_{rec_125}；a_{sw_25}、b_{sw_25}、c_{sw_25}Represent the parameter determined by 25 DEG C of energy consumption curve matchings, be fitted obtaining a to IGBT turn-on consumption curve_{on_25}、b_{on_25}、c_{on_25}, it is fitted obtaining a to IGBT turn-off power loss curve_{off_25}、b_{off_25}、c_{off_25}, it is fitted obtaining a to diode reverse recovery losses curve_{rec_25}、b_{rec_25}、c_{rec_25}。

Step 3: calculate the average switch loss of single power device:

Corresponding switching loss energy is added up by the number of times according to switch motion, then it is carried out time average, can obtain the average switch loss of each several part.Such as, in submodule as shown in Figure 2, the computing formula of the reverse blocking loss of the turn-on consumption of T1 and turn-off power loss, D1 is as follows:

$P_{T1\mathrm{on}}=\frac{1}{T_s}\·{\mathrm{\Σ}}_{u=1}^w\left(\frac{u_{\mathrm{dc}}}{v_{\mathrm{ceref}}}{E}_{\mathrm{onTju}}\right)---\left(7\right);$

$P_{T1\mathrm{off}}=\frac{1}{T_s}\·{\mathrm{\Σ}}_{u=1}^w\left(\frac{u_{\mathrm{dc}}}{v_{\mathrm{ceref}}}{E}_{\mathrm{offTju}}\right)---\left(8\right);$

$P_{D1\mathrm{rec}}=\frac{1}{T_s}\·{\mathrm{\Σ}}_{u=1}^w\left(\frac{u_{\mathrm{dc}}}{v_{\mathrm{ceref}}}{E}_{\mathrm{recTju}}\right)---\left(9\right);$

Wherein: u_dcFor submodule capacitor voltage；v_cerefFor the reference voltage base value in order to calculate switching loss that producer provides；E_onTjuFor T1 at working junction temperature T_jThe loss of energy of generation is opened for the u time at DEG C；E_offTjuFor T1 at working junction temperature T_jThe loss of energy produced is turned off the u time at DEG C；E_recTjuFor D1 at working junction temperature T_jThe loss of energy of the u time reverse blocking generation at DEG C；T_sFor the MMC-DC/AC/DC changer AC working cycle；W is T_sThe number of times of switch in cycle time.

Step 4: determine the distribution situation of switching loss type in MMC-DC/AC/DC changer ac cycle

Step 4.1: determine that single half-bridge submodule produces the condition of different switching loss type:

Half-bridge sub modular structure is as in figure 2 it is shown, the switching change over order of bridge arm current direction and submodule all affects switching loss situation.Such as, when bridge arm current direction is just, submodule has input state to become to produce the turn-on consumption of T2 and the reverse blocking loss of D1 in excision state procedure.Enumerate all situations as shown in table 1.

The switching loss situation of the single half-bridge submodule of table 1

Step 4.2: determine the switching loss type of the upper and lower brachium pontis of MMC inverter:

According to MMC-DC/AC/DC changer operation mechanism, shown in the expression formula of upper and lower bridge arm voltage and electric current such as formula (10)-(13), considering that in DC/AC/DC changer, the reactive power of transmission is only small, the power factor of input/output terminal MMC all can reach significantly high, namelyFig. 5 and 6 are the oscillogram of upper and lower bridge arm current and voltage.When brachium pontis output voltage rises, part brachium pontis submodule is input state by excising State Transferring, produces corresponding switching loss according to bridge arm current direction；When brachium pontis output voltage declines, part brachium pontis submodule is input state by excising State Transferring.Associative list 1, Fig. 5 and Fig. 6, can obtain the distribution situation of the switching loss of upper and lower brachium pontis, as shown in table 2 and Fig. 6.Owing to T1 and T2, D1 and D2 model is consistent, produced switching loss size is only relevant with bridge arm current, does not subdivide the switching loss specifically produced by which switching device herein.

$U_{\mathrm{up}}=\frac{U_d}{2}-U_m\cos \mathrm{\θ}=\frac{U_d}{2}(1-m\·\cos \mathrm{\θ})---\left(10\right);$

$U_{\mathrm{down}}=\frac{U_d}{2}+U_m\cos \mathrm{\θ}=\frac{U_d}{2}(1+m\·\cos \mathrm{\θ})---\left(11\right);$

Table 2 upper and lower bridge arm switching loss distribution situation

Wherein: U_upFor upper brachium pontis output voltage；U_downFor lower brachium pontis output voltage；U_dFor DC voltage；U_mFor MMC-DC/AC/DC changer AC output voltage peak value；θ is the phase angle of alternating voltage；M is voltage modulated degree；i_upFor upper bridge arm current；i_downFor lower bridge arm current；I_dFor MMC Converter DC-side electric current；I_mFor ac-side current peak value；Phase angle difference for AC voltage Yu electric current；As shown in Fig. 5 dotted line, wherein θ₁、θ₂Zero crossing for upper bridge arm current；i_downFor lower bridge arm current, as Fig. 5 is shown in solid, wherein θ '₁、θ′₂Zero crossing for lower bridge arm current；

Step 5: calculate the average switch loss of the single-phase upper and lower brachium pontis of input MMC inverter

Step 5.1: switching loss is carried out equivalent replacement

A phase in input MMC inverter.Curve A in Fig. 6₁A₂Interior lower brachium pontis produces turn-on consumption and reverse blocking loss, curve A₅A₆Interior lower brachium pontis produces turn-off power loss.Due to curve A₁A₂And A₅A₆The size of corresponding bridge arm current is identical and brachium pontis output voltage is identical, when ensureing that in the primitive period, switching loss summation is constant, it is believed that curve A₁A₂Corresponding lower brachium pontis A₅A₆The turn-off power loss produced in time period, curve A₅A₆Corresponding lower brachium pontis A₁A₂The turn-on consumption produced in time period and reverse blocking loss.In like manner, by curve A₂A₃And A₄A₅Interior loss is replaced, by curve B₁A₂And A₅B₆Interior loss displacement, by curve A₂B₃And B₄A₅Interior loss is replaced.Loss after equivalent replacement is distributed as shown in Figure 7.

Step 5.2: calculate the average switch loss of the single-phase upper and lower brachium pontis of input MMC inverter

The switching loss in the primitive period can be solved, as shown in formula (14) according to Fig. 7.

$\begin{array}{c}{P}_{\mathrm{sw}\_1}=\frac{U_{\mathrm{cap}}}{T_s\·U_{\mathrm{ref}}}\left\{{\mathrm{\Σ}}_{h=1}^{N_1}\right[a_{\mathrm{offTj}}+b_{\mathrm{offTj}}(i_{\mathrm{uph}}+i_{\mathrm{downh}})+c_{\mathrm{offTj}}(i_{\mathrm{uph}}^2+i_{\mathrm{downh}}^2)]+\\ {\mathrm{\Σ}}_{i=1}^{N_2}[a_{\mathrm{onrecTj}}+b_{\mathrm{onrecTj}}\·(i_{\mathrm{upi}}+i_{\mathrm{downi}})+c_{\mathrm{onrecTj}}\·(i_{\mathrm{upi}}^2+i_{\mathrm{downi}}^2)]+{\mathrm{\Σ}}_{j=1}^{N_3}[a_{\mathrm{offTj}}+\\ b_{\mathrm{offTj}}(i_{\mathrm{upj}}+i_{\mathrm{downj}})+c_{\mathrm{offTj}}(i_{\mathrm{upj}}^2+i_{\mathrm{downj}}^2)]+{\mathrm{\Σ}}_{k=1}^{N4}[a_{\mathrm{onrecTj}}+b_{\mathrm{onrecTj}}\·(i_{\mathrm{upk}}+\\ i_{\mathrm{downk}})+c_{\mathrm{onrecTj}}\·(i_{\mathrm{upk}}^2+i_{\mathrm{downk}}^2)\left]\right\}\end{array}---\left(14\right);$

a_onrecTj=a_onTj+a_recTj(15)；

b_onrecTj=b_onTj+b_recTj(16)；

c_onrecTj=c_onTj+c_recTj(17)；

Wherein: P_{sw_1}For the switching loss of power device in the single-phase upper and lower brachium pontis of MMC inverter；N1 represent [0, pi/2) interior brachium pontis submodule switching conversion number of times；N2 represent [pi/2, π) interior brachium pontis submodule switching conversion number of times；N3 represent [π, 3 pi/2s) interior brachium pontis submodule switching conversion number of times；N4 represent [3 pi/2s, 2 π) interior brachium pontis submodule switching conversion number of times；i_uphAnd i_downhFor [0, pi/2) conversion of the h time switching of interior brachium pontis time corresponding upper bridge arm current and lower bridge arm current；i_upiAnd i_downiFor [pi/2, π) conversion of interior brachium pontis i & lt switching time corresponding upper bridge arm current and lower bridge arm current；i_upjAnd i_downjFor [π, 3 pi/2s) conversion of interior brachium pontis jth time switching time corresponding upper bridge arm current and lower bridge arm current；i_upkAnd i_downkFor [3 pi/2s, 2 π) conversion of interior brachium pontis kth time switching time corresponding upper bridge arm current and lower bridge arm current；U_capFor submodule electric capacity rated voltage.

Step 5.3: bring upper and lower bridge arm current expression formula into abbreviation

Upper and lower bridge arm current expression formula (12) and (13) are brought into and are simplified:

$\begin{array}{c}{P}_{\mathrm{sw}\_1}=\frac{U_{\mathrm{cap}}}{T_s\·U_{\mathrm{ref}}}[N_1(a_{\mathrm{offTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{offTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{offTj}})+{\mathrm{\Σ}}_{h=1}^{N_1}{c}_{\mathrm{offTj}}\frac{1}{2}{I}_m^2{\cos }^2{\mathrm{\θ}}_{1h}+\\ N_2(a_{\mathrm{onrecTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{onrecTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{onrecTj}})+{\mathrm{\Σ}}_{i=1}^{N_2}{c}_{\mathrm{onrecTj}}\frac{1}{2}{I}_m^2{\cos }^2{\mathrm{\θ}}_{2i}+\\ N_3(a_{\mathrm{offTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{offTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{offTj}})+{\mathrm{\Σ}}_{j=1}^{N_3}{c}_{\mathrm{offTj}}\frac{1}{2}{I}_m^2{\cos }^2{\mathrm{\θ}}_{3j}+N_4(a_{\mathrm{onrecTj}}+\frac{2}{3}{i}_d\·\\ b_{\mathrm{onrecTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{onrecTj}})+{\mathrm{\Σ}}_{k=1}^{N_4}{c}_{\mathrm{onrecTj}}\frac{1}{2}{I}_m^2{\cos }^2{\mathrm{\θ}}_{4k}]\end{array}---\left(18\right);$

Step 5.4: utilize the quantitative relationship that modulation strategy is corresponding to simplify the analytical expression of average switch loss

Assuming that upper and lower brachium pontis Neutron module number is more, and number is n, nearest level approach modulation strategy and obtain, upper and lower brachium pontis reference voltage compares with a series of threshold voltage values, generates and modulates signal accordingly.Threshold voltage is respectively as follows: 0,N+1 altogether.Each θ_1h、θ_2i、θ_3j、θ_4kFor the angle that bridge arm voltage modulating wave is corresponding with threshold voltage intersection, can obtain analytical expression is (19)-(22), and signal is as shown in Figure 8.And formula (19)-(22) are brought into formula (18) relational expression (24), through ordered series of numbers summation obtain formula (25).

$\frac{U_d}{2}-U_m\cos {\mathrm{\θ}}_{1h}=\left(\right[\frac{n\·(1-m)}{2}]+h-1)\·\frac{U_d}{n};h=\mathrm{1,2},...N_1---\left(19\right);$

$\frac{U_d}{2}-U_m\cos {\mathrm{\θ}}_{2i}=(\frac{n}{2}+h-1)\·\frac{U_d}{n};i=\mathrm{1,2}...N_2---\left(20\right);$

$\frac{U_d}{2}-U_m\cos {\mathrm{\θ}}_{3j}=(n-[\frac{n\·(1-m)}{2}]-h-1)\·\frac{U_d}{n};j=\mathrm{1,2},...N_3---\left(21\right);$

$\frac{U_d}{2}-U_m\cos {\mathrm{\θ}}_{4k}=(\frac{n}{2}-h-1)\·\frac{U_d}{n};k=\mathrm{1,2}...N_4---\left(22\right);$

$N_1=N_2=N_3=N_4=(\frac{n}{2}-[\frac{n\·(1-m)}{2}\left]\right)=\frac{n}{2}-Q---\left(23\right);$

$\begin{array}{c}{P}_{\mathrm{sw}\_1}=\frac{U_{\mathrm{cap}}}{T_s\·U_{\mathrm{ref}}}\{N_1(a_{\mathrm{offTj}}+\frac{2}{3}{i}_d\·d_{\mathrm{offTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{offTj}})+\frac{c_{\mathrm{offTj}}}{2}\·I_m^2\·{\left(\frac{U_d}{U_m}\right)}^2\·[{(\frac{1}{2}-\frac{Q}{n})}^2+\\ {(\frac{1}{2}-\frac{Q+1}{n})}^2+...+{(\frac{1}{2}-\frac{\frac{n}{2}-1}{2})}^2]+N_2(a_{\mathrm{onrecTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{onrecTj}}+\frac{2}{9}\·c_{\mathrm{onrecTj}})+\\ \frac{c_{\mathrm{onrecTj}}}{2}\·I_m^2\·{\left(\frac{U_d}{U_m}\right)}^2\·[{\left(\frac{1}{n}\right)}^2+{\left(\frac{2}{n}\right)}^2+...+{(\frac{1}{2}-\frac{Q}{n})}^2]+N_3(a_{\mathrm{offTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{offTj}}+\frac{2}{9}\·i_d^2\·\\ c_{\mathrm{offTj}})+\frac{c_{\mathrm{offTj}}}{2}\·I_m^2\·{\left(\frac{U_d}{U_m}\right)}^2\·{[\left(\frac{1}{n}\right)}^2+{\left(\frac{2}{n}\right)}^2+...+{(\frac{1}{2}-\frac{Q}{n})}^2]+N_4(a_{\mathrm{onrecTj}}+\frac{2}{3}{i}_d\·)\\ b_{\mathrm{onrecTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{onrecTj}})+\frac{c_{\mathrm{onrecTj}}}{2}\·I_m^2\·{\left(\frac{U_d}{U_m}\right)}^2\·[{\left(\frac{1}{n}\right)}^2+{\left(\frac{2}{n}\right)}^2+...+{(\frac{1}{2}-\frac{Q}{n})}^2]\}\end{array}---\left(24\right);$

$\begin{array}{c}{P}_{\mathrm{sw}\_1}=\frac{U_{\mathrm{cap}}}{T_s\·U_{\mathrm{ref}}}\{(n-2Q)\·(a_{\mathrm{onoffrecTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{onoffrecTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{onoffrecTj}})+\\ c_{\mathrm{onoffrecTj}}\·I_m^2\·{\left(\frac{1}{m}\right)}^2\·\frac{1}{12n^2}(n-2Q)(n-2Q+1)\·(n-2Q+2)\}\end{array}---\left(25\right);$

a_onoffrecTj=a_onTj+a_offTj+a_recTj(26)；

b_onoffrecTj=b_onTj+b_offTj+b_recTj(27)；

c_onoffrecTj=c_onTj+c_offTj+c_recTj(28)；

Wherein: [], for rounding algorithm, Q represents bracket function, the different voltage modulated degree impact on loss of reaction；H represent (0, pi/2] in the number of times that intersects with threshold voltage of bridge arm voltage modulating wave；a_onoffrecTj、b_onoffrecTj、c_onoffrecTjRepresent the sum of IGBT turn-on consumption, turn-off power loss and diode reverse cut-off loss curve fitting parameter when junction temperature is Tj respectively.

Step 6: calculate the switching loss of all power devices of MMC-DC/AC/DC changer

Step 6.1: calculate the switching loss of input MMC inverter three phase power device

Due to MMC inverter symmetrical operation, the switching loss of input MMC inverter three phase power device can be solved according to step 5, as shown in formula (29).

P_{sw_3}=3*P_{sw_1}(29)；

Step 6.2: calculate the switching loss of outfan MMC inverter three phase power device

Adopt step 5 and 6.1 same methods, it is possible to ask for the switching loss of outfan MMC inverter three phase power device, as shown in formula (30).

P′_{sw_3}=3*P '_{sw_1}(30)；

Step 6.2: calculate the switching loss of all power devices in MMC-DC/AC/DC changer

The switching loss of input and outfan MMC in step 6.1 and 6.2 is added to obtain the switching loss of all power devices in MMC-DC/AC/DC changer, as shown in formula (31).

P_total=P_{sw_3}+P′_{sw_3}(31)；

Wherein: P_totalSwitching loss for power devices all in MMC-DC/AC/DC changer.

Finally should be noted that: above example is only in order to illustrate that technical scheme is not intended to limit; although the present invention being described in detail with reference to above-described embodiment; the specific embodiment of the present invention still can be modified or equivalent replacement by those of ordinary skill in the field; these are without departing from any amendment of spirit and scope of the invention or equivalent replace, within the claims of the present invention all awaited the reply in application.

Claims (7)

1., based on a defining method for MMC isolated form DC/DC converter switches loss, described isolated form DC/DC changer includes isolating transformer and the MMC of two ends connection thereof；Two MMC all access in straight-flow system；Modularization multi-level converter MMC is made up of three-phase, is often made up of upper and lower two brachium pontis that the structure connected is identical；The exchange end of the midpoint connection mode massing multilevel converter of upper and lower two brachium pontis；

In described upper and lower two brachium pontis, each brachium pontis includes 1 reactor submodule identical with N number of structure；After the sub module cascade of each brachium pontis, one end is connected with the exchange end of modularization multi-level converter by reactor；After the sub module cascade of each brachium pontis, the other end is connected with submodule one end of the cascade of two other phase brachium pontis, forms the both positive and negative polarity bus of modular multilevel voltage source converter DC terminal；Described submodule is made up of the capacitor branches that half-bridge is connected in parallel, and described half-bridge is made up of upper brachium pontis and lower brachium pontis, and described upper brachium pontis and lower brachium pontis form by insulated gate bipolar transistor IGBT and fly-wheel diode FWD connected in parallel；

It is characterized in that, described method comprises the steps:

Step 1: the switching loss characteristics of MMC Neutron module power device is carried out parameter fitting；

Step 2: utilize the switching loss energy of submodule power device under interpolation calculation working junction temperature；

Step 3: determine the average switch loss of single power device；

Step 4: determine the distribution of switching loss type in MMC-DC/AC/DC changer ac cycle；

Step 5: determine the average switch loss of the single-phase upper and lower brachium pontis of input MMC inverter；

Step 6: determine the switching loss of all power devices of MMC-DC/AC/DC changer.

2. defining method as claimed in claim 1, it is characterized in that, in described step 1, for the power device switching loss characteristics in submodule, adopt the quadratic polynomial such as following formula (1) to intend united extraction switching loss characterisitic parameter, ask for the energy loss of once switch motion on given on state current:

Wherein: E_{sw_k}Represent junction temperature be k DEG C at the opening of IGBT, turn off or the reverse recovery loss (E of diode_on, E_offOr E_rec)；i_devRepresent the electric current flowing through power device, be collector current i for IGBT_C, it is forward current i for diode_F；a_{sw_k}、b_{sw_k}、c_{sw_k}It is the parameter determined by 25 DEG C and 125 DEG C of energy consumption curve matchings respectively, is fitted obtaining a to IGBT turn-on consumption curve_{on_k}、b_{on_k}、c_{on_k}, it is fitted obtaining a to IGBT turn-off power loss curve_{off_k}、b_{off_k}、c_{off_k}, it is fitted obtaining a to diode reverse recovery losses curve_{rec_k}、b_{rec_k}、c_{rec_k}。

3. defining method as claimed in claim 1, it is characterised in that in described step 2, according to the energy consumption curve fitting result of power device in 25 DEG C and 125 DEG C of submodules, utilize interpolation calculation working junction temperature T_jThe switching loss energy of power device in submodule at DEG C, as shown in following formula (2)；Bring formula (1) into formula (2) and carry out abbreviation, obtain formula (3)-(6):

$E_{\mathrm{swTj}}=(E_{\mathrm{sw}\_125}-E_{\mathrm{sw}\_25})\·\frac{T_j-25}{100}+E_{\mathrm{sw}\_25}---\left(2\right);$

$E_{\mathrm{swTj}}=a_{\mathrm{swTj}}+b_{\mathrm{swTj}}\·i_{\mathrm{dev}}+c_{\mathrm{swTj}}\·i_{\mathrm{dev}}^2---\left(3\right);$

$a_{\mathrm{swTj}}=(a_{\mathrm{sw}\_125}-a_{\mathrm{sw}\_25})\·\frac{T_j-25}{100}+a_{\mathrm{sw}\_25}---\left(4\right);$

$b_{\mathrm{swTj}}=(b_{\mathrm{sw}\_125}-b_{\mathrm{sw}\_25})\·\frac{T_j-25}{100}+b_{\mathrm{sw}\_25}---\left(5\right);$

$c_{\mathrm{swTj}}=(c_{\mathrm{sw}\_125}-c_{\mathrm{sw}\_25})\·\frac{T_j-25}{100}+c_{\mathrm{sw}\_25}---\left(6\right);$

Wherein: E_swTjRepresent junction temperature be Tj DEG C at the switching loss energy of power device in submodule；a_swTj、b_swTj、c_swTj, respectively junction temperature be Tj DEG C at the parameter in the switching loss expression formula of power device in submodule；E_{sw_125}Represent that junction temperature is the opening of IGBT at 125 DEG C, turns off or the reverse recovery loss of diode；E_{sw_25}Represent that junction temperature is the opening of IGBT at 25 DEG C, turns off or the reverse recovery loss of diode；a_{sw_125}、b_{sw_125}、c_{sw_125}Represent the parameter determined by 125 DEG C of energy consumption curve matchings, be fitted obtaining a to IGBT turn-on consumption curve_{on_125}、b_{on_125}、c_{on_125}, it is fitted obtaining a to IGBT turn-off power loss curve_{off_125}、b_{off_125}、c_{off_125}, it is fitted obtaining a to diode reverse recovery losses curve_{rec_125}、b_{rec_125}、c_{rec_125}；a_{sw_25}、b_{sw_25}、c_{sw_25}Represent the parameter determined by 25 DEG C of energy consumption curve matchings, be fitted obtaining a to IGBT turn-on consumption curve_{on_25}、b_{on_25}、c_{on_25}, it is fitted obtaining a to IGBT turn-off power loss curve_{off_25}、b_{off_25}、c_{off_25}, it is fitted obtaining a to diode reverse recovery losses curve_{rec_25}、b_{rec_25}、c_{rec_25}。

4. defining method as claimed in claim 1, it is characterized in that, in described step 3, according to the number of times turned on and off of power device in submodule, corresponding switching loss energy is added up, it is carried out time average, the average switch loss of each several part can be obtained；The turn-on consumption P of IGBTT1 in submodule_T1onWith turn-off power loss P_T1offAnd the reverse blocking loss P of diode D1_D1recComputing formula as follows:

$P_{T1\mathrm{on}}=\frac{1}{T_s}\·{\mathrm{\Σ}}_{u=1}^w\left(\frac{u_{\mathrm{dc}}}{v_{\mathrm{ceref}}}{E}_{\mathrm{onTju}}\right)---\left(7\right);$

$P_{T1\mathrm{off}}=\frac{1}{T_s}\·{\mathrm{\Σ}}_{u=1}^w\left(\frac{u_{\mathrm{dc}}}{v_{\mathrm{ceref}}}{E}_{\mathrm{offTju}}\right)---\left(8\right);$

$P_{D1\mathrm{rec}}=\frac{1}{T_s}\·{\mathrm{\Σ}}_{u=1}^w\left(\frac{u_{\mathrm{dc}}}{v_{\mathrm{ceref}}}{E}_{\mathrm{recTju}}\right)---\left(9\right);$

Wherein: u_dcFor submodule capacitor voltage；v_cerefFor the reference voltage base value in order to calculate switching loss that producer provides；E_onTjuFor IGBTT1 at working junction temperature T_jThe loss of energy of generation is opened for the u time at DEG C；E_offTjuFor IGBTT1 at working junction temperature T_jThe loss of energy produced is turned off the u time at DEG C；E_recTjuFor D1 at working junction temperature T_jThe loss of energy of the u time reverse blocking generation at DEG C；T_sFor the MMC-DC/AC/DC changer AC working cycle；W is T_sThe number of times of switch in cycle time.

5. defining method as claimed in claim 1, it is characterised in that described step 4 comprises the steps:

Step 4.1: determine that single half-bridge submodule produces the condition of different switching loss type:

For half-bridge sub modular structure, the switching change over order of bridge arm current direction and submodule all affects switching loss type；When bridge arm current direction is just, submodule has input state to become producing the turn-on consumption of IGBTT2 and the reverse blocking loss of diode D1 in excision state procedure；

Step 4.2: determine MMC inverter upper and lower brachium pontis breaker in middle loss type:

According to MMC-DC/AC/DC changer operation mechanism, shown in the expression formula of upper and lower bridge arm voltage and electric current such as formula (10)-(13)；When brachium pontis output voltage rises, part brachium pontis submodule is input state by excising State Transferring, produces corresponding switching loss according to bridge arm current direction；When brachium pontis output voltage declines, part brachium pontis submodule is input state by excising State Transferring:

$U_{\mathrm{up}}=\frac{U_d}{2}-U_m\cos \mathrm{\θ}=\frac{U_d}{2}(1-m\·\cos \mathrm{\θ})---\left(10\right);$

$U_{\mathrm{down}}=\frac{U_d}{2}+U_m\cos \mathrm{\θ}=\frac{U_d}{2}(1+m\·\cos \mathrm{\θ})---\left(11\right)$

Wherein: U_upFor upper brachium pontis output voltage；U_downFor lower brachium pontis output voltage；U_dFor DC voltage；U_mFor MMC-DC/AC/DC changer AC output voltage peak value；θ is the phase angle of alternating voltage；M is voltage modulated degree；i_upFor upper bridge arm current, I_dFor MMC Converter DC-side electric current；I_mFor ac-side current peak value；Phase angle difference for AC voltage Yu electric current；K is current-modulation degree.

6. defining method as claimed in claim 1, it is characterised in that described step 5 comprises the steps:

Step 5.1: switching loss is carried out equivalent replacement so that the switchtype that upper and lower brachium pontis produces at synchronization is consistent；

Step 5.2: calculate the average switch loss of the single-phase upper and lower brachium pontis of input MMC inverter:

Solve the switching loss in the primitive period, as shown in following formula (14):

$\begin{array}{c}{P}_{\mathrm{sw}\_1}=\frac{U_{\mathrm{cap}}}{T_s\·U_{\mathrm{ref}}}\left\{{\mathrm{\Σ}}_{h=1}^{N_1}\right[a_{\mathrm{offTj}}+b_{\mathrm{offTj}}(i_{\mathrm{uph}}+i_{\mathrm{downh}})+c_{\mathrm{offTj}}(i_{\mathrm{uph}}^2+i_{\mathrm{downh}}^2)]+\\ {\mathrm{\Σ}}_{i=1}^{N_2}[a_{\mathrm{onrecTj}}+b_{\mathrm{onrecTj}}\·(i_{\mathrm{upi}}+i_{\mathrm{downi}})+c_{\mathrm{onrecTj}}\·(i_{\mathrm{upi}}^2+i_{\mathrm{downi}}^2)]+{\mathrm{\Σ}}_{j=1}^{N_s}[a_{\mathrm{offTj}}+\\ b_{\mathrm{offTj}}(i_{\mathrm{upj}}+i_{\mathrm{downj}})+c_{\mathrm{offTj}}(i_{\mathrm{upj}}^2+i_{\mathrm{downj}}^2)]+{\mathrm{\Σ}}_{k=1}^{N_4}[a_{\mathrm{onrecTj}}+b_{\mathrm{onrecTj}}\·(i_{\mathrm{upk}}+\\ i_{\mathrm{downk}})+c_{\mathrm{onrecTj}}\·(i_{\mathrm{upk}}^2+i_{\mathrm{downk}}^2)\left]\right\}\end{array}---\left(14\right);$

a_onrecTj=a_onTj+a_recTj(15)；

b_onrecTj=b_onTj+b_recTj(16)；

c_onrecTj=c_onTj+c_recTj(17)；

Wherein: P_{sw_1}For the switching loss of power device in the single-phase upper and lower brachium pontis of MMC inverter；N1 represent [0, pi/2) interior brachium pontis submodule switching conversion number of times；N2 represent [pi/2, π) interior brachium pontis submodule switching conversion number of times；N3 represent [π, 3 pi/2s) interior brachium pontis submodule switching conversion number of times；N4 represent [3 pi/2s, 2 π) interior brachium pontis submodule switching conversion number of times；i_uphAnd i_downhFor [0, pi/2) conversion of the h time switching of interior brachium pontis time corresponding upper bridge arm current and lower bridge arm current；i_upiAnd i_downiFor [pi/2, π) conversion of interior brachium pontis i & lt switching time corresponding upper bridge arm current and lower bridge arm current；i_upjAnd i_downjFor [π, 3 pi/2s) conversion of interior brachium pontis jth time switching time corresponding upper bridge arm current and lower bridge arm current；i_upkAnd i_downkFor [3 pi/2s, 2 π) conversion of interior brachium pontis kth time switching time corresponding upper bridge arm current and lower bridge arm current；U_capFor submodule electric capacity rated voltage；a_onrecTj、b_onrecTj、c_onrecTjRepresent the sum of IGBT turn-on consumption curve and diode reverse cut-off loss curve fitting parameter under Tj junction temperature respectively；T_sFor the MMC-DC/AC/DC changer AC working cycle；

Step 5.3: bring upper and lower bridge arm current expression formula (12) and (13) into formula (14) and simplify:

$\begin{array}{c}{P}_{\mathrm{sw}\_1}+\frac{U_{\mathrm{cap}}}{T_s\·U_{\mathrm{ref}}}[N_1(a_{\mathrm{offTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{offTj}}+\frac{2}{9}\·i_2^d\·c_{\mathrm{offTj}})+{\mathrm{\Σ}}_{h=1}^{N_1}{c}_{\mathrm{offTj}}\frac{1}{2}{I}_m^2{\cos }^2{\mathrm{\θ}}_{1h}+\\ N_2(a_{\mathrm{onrecTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{onrecTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{onrecTj}})+{\mathrm{\Σ}}_{i=1}^{N_2}{c}_{\mathrm{onrecTj}}\frac{1}{2}{I}_m^2{\cos }^2{\mathrm{\θ}}_{2i}+\\ N_3(a_{\mathrm{offTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{offTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{offTj}})+{\mathrm{\Σ}}_{j=1}^{N_s}{c}_{\mathrm{offTj}}\frac{1}{2}{I}_m^2{\cos }^2{\mathrm{\θ}}_{3j}+N_4(a_{\mathrm{onrecTj}}+\frac{2}{3}{i}_d\·\\ b_{\mathrm{onrecTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{onrecTj}})+{\mathrm{\Σ}}_{k=1}^{N_4}{c}_{\mathrm{onrecTj}}\frac{1}{2}{I}_m^2{\cos }^2{\mathrm{\θ}}_{4k}]\end{array}---\left(18\right);$

Step 5.4: utilize the quantitative relationship that modulation strategy is corresponding to simplify average switch loss:

Assuming that in half-bridge submodule, upper and lower brachium pontis Neutron module number is n, is approached modulation strategy by nearest level and obtains, upper and lower brachium pontis reference voltage compares with threshold voltage value, generates and modulates signal accordingly；Threshold voltage is respectively as follows:N+1 altogether, θ_1hRepresent bridge arm voltage modulating wave (0, pi/2] in the h time angle corresponding with threshold voltage intersection；θ_2iRepresent bridge arm voltage modulating wave (pi/2, π] the interior i & lt angle corresponding with threshold voltage intersection；θ_3jRepresent bridge arm voltage modulating wave [π, 3 pi/2s) time corresponding with the threshold voltage intersection angle of interior jth；θ_4kRepresent bridge arm voltage modulating wave [3 pi/2s, 2 π) time corresponding with the threshold voltage intersection angle of interior kth；Obtain analytical expression (19)-(22), and formula (19)-(22) are brought into formula (18) relational expression (24), obtain formula (25) through ordered series of numbers summation:

$\frac{U_d}{2}-U_m\cos {\mathrm{\θ}}_{1h}=\left(\right[\frac{n\·(1-m)}{2}]+h-1)\·\frac{U_d}{n};h=\mathrm{1,2}...N_1---\left(19\right);$

$\frac{U_d}{2}-U_m\cos {\mathrm{\θ}}_{2i}=(\frac{n}{2}+h-1)\·\frac{U_d}{n};i=\mathrm{1,2}...N_2---\left(20\right);$

$\frac{U_d}{2}-U_m\cos {\mathrm{\θ}}_{3j}=(n-[\frac{n\·(1-m)}{2}]-h-1)\·\frac{U_d}{n};j=\mathrm{1,2}...N_3---\left(21\right);$

$\frac{U_d}{2}-U_m\cos {\mathrm{\θ}}_{4k}=(\frac{n}{2}-h-1)\·\frac{U_d}{n};k=\mathrm{1,2}...N_4---\left(22\right);$

$N_1=N_2=N_3=N_4=(\frac{n}{2}-[\frac{n\·(1-m)}{2}\left]\right)=\frac{n}{2}-Q---\left(23\right);$

$\begin{array}{c}{P}_{\mathrm{sw}\_1}=\frac{U_{\mathrm{cap}}}{T_s\·U_{\mathrm{ref}}}\{N_1(a_{\mathrm{offTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{offTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{offTj}})+\frac{c_{\mathrm{offTj}}}{2}\·I_m^2\·{\left(\frac{U_d}{U_m}\right)}^2\·[{(\frac{1}{2}-\frac{Q}{n})}^2+\\ {(\frac{1}{2}-\frac{Q+1}{n})}^2+...+{\left(\frac{1}{2}\frac{\frac{n}{2}-1}{2}\right)}^2]+N_2(a_{\mathrm{onrecTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{onrecTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{onrecTj}})+\\ \frac{c_{\mathrm{onrecTj}}}{2}\·I_m^2\·{\left(\frac{U_d}{U_m}\right)}^2\·[{\left(\frac{1}{n}\right)}^2+{\left(\frac{2}{n}\right)}^2+...+{(\frac{1}{2}-\frac{Q}{n})}^2]+N_3(a_{\mathrm{offTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{offTj}}+\frac{2}{9}\·i_d^2\·\\ c_{\mathrm{offTj}})+\frac{c_{\mathrm{offTj}}}{2}\·I_m^2\·{\left(\frac{U_d}{U_m}\right)}^2\·[{\left(\frac{1}{n}\right)}^2+{\left(\frac{2}{n}\right)}^2+...+{(\frac{1}{2}-\frac{Q}{n})}^2]+N_4(a_{\mathrm{onrecTj}}+\frac{2}{3}{i}_d\·\\ b_{\mathrm{onrecTj}}+\frac{2}{9}\·i_d^2\·c_{\mathrm{onrecTj}})+\frac{c_{\mathrm{onrecTj}}}{2}\·I_m^2\·{\left(\frac{U_d}{U_m}\right)}^2\·[{\left(\frac{1}{n}\right)}^2+{\left(\frac{2}{n}\right)}^2+...+{(\frac{1}{2}-\frac{Q}{n})}^2]\}\end{array}---\left(24\right);$

$\begin{array}{c}{P}_{\mathrm{sw}\_1}=\frac{U_{\mathrm{cap}}}{T_s\·U_{\mathrm{ref}}}\{(n-2Q)\·(a_{\mathrm{onoffrecTj}}+\frac{2}{3}{i}_d\·b_{\mathrm{onoffrecTj}}+\frac{2}{9}{\·i}_d^2\·c_{\mathrm{onoffrecTj}})+\\ c_{\mathrm{onoffrecTj}}\·I_m^2\·{\left(\frac{1}{m}\right)}^2\·\frac{1}{{12n}^2}(n-2Q)(n-2Q+1)\·(n-2Q+2)\}\end{array}---\left(25\right);$

a_onoffrecTj=a_onTj+a_offTj+a_recTj(26)；

b_onffrecTj=b_onTj+b_offTj+b_recTj(27)；

c_onoffrecTj=c_onTj+c_offTj+c_recTj(28)；

Wherein: [], for rounding algorithm, Q represents bracket function, the different voltage modulated degree impact on loss of reaction；H represent (0, pi/2] in the number of times that intersects with threshold voltage of bridge arm voltage modulating wave；a_onoffrecTj、b_onoffrecTj、c_onoffrecTjRepresent the sum of IGBT turn-on consumption, turn-off power loss and diode reverse cut-off loss curve fitting parameter when junction temperature is Tj respectively.

7. defining method as claimed in claim 1, it is characterised in that described step 6 comprises the steps:

Step 6.1: calculate the switching loss of input MMC inverter three phase power device；

MMC inverter symmetrical operation, solves the switching loss of input MMC inverter three phase power device, as shown in following formula (29) according to step 5:

P_{sw_3}=3*P_{sw_1}(29)；

Step 6.2: calculate the switching loss of outfan MMC inverter three phase power device: as shown in following formula (30):

P′_{sw_3}=3*P '_{sw_1}(30)；

Step 6.2: calculate the switching loss of all power devices in MMC-DC/AC/DC changer

The switching loss of input and outfan MMC in step 6.1 and 6.2 is added to obtain the switching loss of all power devices in MMC-DC/AC/DC changer, as shown in following formula (31):

P_total=P_{sw_3}+P′_{sw_3}(31)；

Wherein: P_totalSwitching loss for power devices all in MMC-DC/AC/DC changer.