CN102013825B - Loss analysis method for diode clamping type three-level voltage source converter (VSC) - Google Patents

Abstract

The invention provides a loss analysis method for a diode clamping type three-level voltage source converter (VSC). The method comprises the following steps of: 1) analyzing the conduction rule of the diode clamping type three-level VSC, and building a polynomial loss model of an insulated gate bipolar transistor (IGBT); 2) representing the conduction voltage drop and the switching loss of the IGBT as a quadratic polynomial of the current; and 3) calculating the device loss by a polynomial fitting method. According to the method, the loss is simply and rapidly calculated by the polynomial fitting method; and on the basis, the loss variation along with the power factor and the modulation degree and the loss distribution of each device of different operating points are analyzed, so the method provides the basis for parameter selection and thermal design of the device and has greater practical value.

Description

Diode clamp formula three-level voltage source converter loss analysis method

Technical field

The present invention is a kind of for analyzing the loss distribution of each device along with the diode clamp formula three-level voltage source converter loss analysis method of the situation of change of power factor and modulation degree, belongs to the renovation technique of diode clamp formula three level VSC loss analysis methods.

Background technology

Diode clamp type (Diode Clamped, be called again neutral-point-clamped formula Neutral Point Clamped) three-level voltage source converter (Voltage Source Converter, be called for short VSC) structure of main circuit, compared with striding capacitance clamping type three-level converter, diode clamp type three-level converter has significant competitiveness.The cost of clamp diode is lower than the cost of striding capacitance, be easy to encapsulation, and control method is simple, in a lot of fields, is widely applied at present.Power loss affects efficiency and the economical operation of voltage source converter, is a problem must paying close attention in practical engineering application.

Loss evaluation is an important evidence of inverter system design, device parameters selection and thermal design.The IGBT loss model that Chinese scholars is set up mainly concentrates on the loss model of physical structure.It is not too easy that loss model based on physical structure will be applied in actual production, and particularly the definite of model parameter is the process of a more complicated, concerning general user, has certain difficulty.

Summary of the invention

The object of the invention is to consider the problems referred to above and provide a kind of simple and convenient, the diode clamp formula three-level voltage source converter loss analysis method of Fast Practical.The present invention provides foundation to selection and the thermal design of device parameters.

Technical scheme of the present invention is: diode clamp formula three-level voltage source converter loss analysis method of the present invention, and it includes following steps:

1) analyze the conducting rule of diode clamp formula three-level voltage source converter, set up the multinomial loss model of IGBT;

2) conduction voltage drop of IGBT and switching loss are expressed as to the quadratic polynomial of electric current;

3) adopt the method for fitting of a polynomial to carry out the loss of calculating device.

Above-mentioned steps 3) by following concrete steps, undertaken:

A. the user's manual providing according to IGBT manufacturer, adopts the method for fitting of a polynomial to obtain the characteristic curve of IGBT;

B. analyze the conducting rule of diode clamp formula three-level voltage source converter, obtain the conducting duty ratio of each switching tube;

C. the on-state loss of switching device calculates:

Because diode clamp type three-level converter structure is symmetrical, each IGBT module of conventionally selecting is identical with clamp diode characteristic, therefore only need the loss of 4 main switch VT1, VT2, VD3, VD4 and clamp diode VD5 wherein to analyze,

D. the switching loss of switching device is calculated

The computing formula of switching loss is

In formula t _o-power frequency period, t _s -switch periods;

Can obtain thus the switching loss P of VT1 _t1sw, the reverse recovery loss P of VD5 _d5rec, the switching loss P of VT2 _t2sw, the reverse recovery loss P of VD4 _d4rec

D. the loss of diode clamp formula three-level voltage source converter is calculated

The loss of diode clamp type three-level converter is mainly the loss of IGBT module, comprise on-state loss and the reverse recovery loss of on-state loss, switching loss and the reverse parallel connection diode of IGBT part, and the on-state loss of clamp diode and reverse recovery loss, on this basis, analyze the situation of change of loss along with power factor and modulation degree.

Above-mentioned voltage source converter ac-side current is sinusoidal waveform, and DC capacitor voltage is balance.

The present invention, owing to adopting the conducting rule of first passing through to analyze diode clamp formula three-level voltage source converter, sets up the multinomial loss model of IGBT; Again the conduction voltage drop of IGBT and switching loss are expressed as to the quadratic polynomial of electric current; And the method that adopts fitting of a polynomial carrys out the method for the loss of calculating device, simple and convenient, Fast Practical.The present invention provides foundation to selection and the thermal design of device parameters.The present invention is a kind of convenient and practical diode clamp formula three-level voltage source converter loss analysis method.

Accompanying drawing explanation

Fig. 1 is the topological structure of single-phase diode-clamped formula three-level voltage source converter.

Left and right two parts of Fig. 2 are respectively the outside on-state loss of IGBT and the switching loss variation diagrams with power factor and modulation degree.

Left and right two parts of Fig. 3 are respectively the outside on-state loss of diode and the reverse recovery loss variation diagrams with power factor and modulation degree.

Left and right two parts of Fig. 4 are respectively the inside on-state loss of IGBT and the switching loss variation diagrams with power factor and modulation degree.

Left and right two parts of Fig. 5 are respectively the inside on-state loss of diode and the reverse recovery loss variation diagrams with power factor and modulation degree.

Left and right two parts of Fig. 6 are respectively the on-state loss of clamping diode and the reverse recovery loss variation diagrams with power factor and modulation degree.

Black in the loss of pillar shown in Fig. 7-10 figure represents on-state loss, white represents switching loss, and five the column losses of 1-5 shown in from left to right represent respectively the loss figure of outside IGBT, outside diode, the inside IGBT, the inside diode and clamping diode.

Fig. 7 is that power factor is that 1 modulation degree is the loss distribution map of 1 o'clock.

Fig. 8 is that power factor is that-1 modulation degree is the loss distribution map of 1 o'clock.

Fig. 9 is that power factor is that 1 modulation degree is the loss distribution map of 0.05 o'clock.

Figure 10 is that power factor is that-1 modulation degree is the loss distribution map of 0.05 o'clock.

In figure, each symbol is: E, DC voltage; m, modulation degree; pf, power factor; P _toutcond, outside IGBT on-state loss; P _toutsw, outside IGBT switching loss; P _doutcond, outside diode on-state loss; P _doutrec, outside diode reverse recovery loss loss; P _tincond, the inside IGBT on-state loss; P _tinsw, the inside IGBT switching loss; P _dincond, the inside diode on-state loss; P _inrec, the inside diode reverse recovery loss loss; P _dnpccond, clamping diode on-state loss; P _dnpcrec, clamping diode reverse recovery loss loss; The IGBT of Tout, outside; The diode of Dout, outside; The IGBT of Tin, the inside; The diode of Din, the inside; Dnpc, clamping diode.

In literary composition, each symbol is: C ₁=C ₂be two DC capacitors, VT1, VT2, VT3, VT4 are 4 main switches, VD1, VD2, VD3, VD4 are 4 fly-wheel diodes, VD5, VD6 are two clamp diodes, VT1 and VT4 are the IGBT of outside, and VT2 and VT3 are the IGBT of the inside, and VD1 and VD4 are the diode of outside, VD2 and VD3 are the diode of the inside u _cEfor on-state voltage drop, ifor ac-side current, e _tswfor switch energy.

Embodiment

Below take electric current as 260A, fundamental frequency 50Hz, switching frequency 1500Hz, junction temperature t _j=125 ℃, direct voltage is 1800V, and the IGBT module of choosing is FF450R17ME3, and clamp diode BYM600A170DN2 is that example describes this method.

The characteristic curve providing according to IGBT and diode user's manual, adopts the method for fitting of a polynomial to obtain on-state voltage drop u _cEwith e _tswexpression formula

The loss of diode clamp type three-level converter is mainly the loss of IGBT module, comprise on-state loss and the reverse recovery loss of on-state loss, switching loss and the reverse parallel connection diode of IGBT part, and the on-state loss of clamp diode and reverse recovery loss.Because diode clamp type three-level converter structure is symmetrical, each IGBT module of conventionally selecting is identical with clamp diode characteristic, therefore only need the loss of 4 main switch VT1, VT2, VD3, VD4 and clamp diode VD5 wherein to analyze,

By the analysis to main circuit conducting principle, obtain the on off state of device, as shown in table 1.

The on off state of table 1 device

Mark	VT1	VT2	VT3	VT4	Output voltage
						P
	1	1	0	0	E/2
						0	0	1	1	0	0
N	0	0	1	1	-E/2

While adopting the stacked PWM modulation of carrier wave homophase, from geometrical relationship, can obtain the duty ratio of VT, VD, i.e. P 0, the duty ratio of VT is d _p= msin ( a+ θ), the duty ratio of VD is d ₀₊=1- d _p; N 0, the duty ratio of VT is d _n=- msin ( a+ θ), the duty ratio of VD is d _0-=1- d _n, as shown in table 2.

The duty ratio of table 2 VD

VT1

VT2

VD3

VD4

VD5

0~π- θ

D

P

1

0

0

1- D P

π- θ-~π

0

1- D N

D N

D N

1- D N

Thus, obtain the computing formula of on-state loss

On off state is P 0, VT1 and the VD5 change of current, and switching loss is mainly the switching loss of VT1 and the reverse recovery loss of VD5.On off state is N 0, VT2 and the VD4 change of current, and switching loss is mainly the switching loss of VT2 and the reverse recovery loss of VD4.

The computing formula of switching loss is

Fig. 2-6 are that the loss of each device is with the situation of change of power factor and modulation degree.Can find out, along with modulation degree mincrease, the duty ratio of VT1 increases, and on-state loss increases; VT2 reduces in the duty ratio of [π-θ-~ π], and on-state loss reduces; The duty ratio of VD3 and VD4 increases, and on-state loss increases; The duty ratio of VD5 reduces, and on-state loss reduces.Along with power factor pfreduce, the ON time of VT1 reduces, and conduction loss reduces; The ON time of VT2 is constant, but the large ON time of duty ratio reduces, and the ON time that duty ratio is little increases, therefore on-state loss reduces; VD3 and VD4 ON time increase, and on-state loss increases; The ON time of VD5 is constant, but variation has occurred for the time of two conducting phase and corresponding duty ratio, therefore on-state loss will change.

Along with power factor pfreduce, the switching range of VT1 and VD5 narrows, and therefore switching loss reduces; It is large that the switching range of VT2 and VD4 becomes, and switching loss increases.

Fig. 7-10 are the loss distribution map of diode clamp type three-level converter at boundary, are respectively modulation degree pf=1, m=1, pf=-1, m=1, pf=1, m=0.05, and pf=-1, m=0.05.

Can find out the least balance of loss distribution map in these four kinds of situations, power factor pf=1, modulation degree m=1 o'clock, that generation loss is maximum was the IGBT of outside; Power factor pf=-1, modulation degree m=1 o'clock, what generation loss was maximum was the diode of outside; Power factor pf=1, when modulation degree is very low, what generation loss was maximum is clamp diode; Power factor pf=-1, modulation degree mwhen very low, that generation loss is maximum is the IGBT of the inside.

The calculating of above-described embodiment shows, the simple and quick practicality of diode clamp formula three level VSC loss analysis method provided by the invention provides foundation to selection and the thermal design of device parameters.

Claims (2)

1. a diode clamp formula three-level voltage source converter loss analysis method, is characterized in that including following steps:

1) set up the multinomial loss model of three-level voltage source converter loss, wherein the loss of diode clamp formula three-level converter comprises on-state loss and the reverse recovery loss of on-state loss, switching loss and the reverse parallel connection diode of IGBT part, and the on-state loss of clamping diode and reverse recovery loss;

2) characteristic curve providing according to IGBT and diode user's manual, adopts the method for fitting of a polynomial by the conduction voltage drop of IGBT and diode and switch energy loss value E _tswbe expressed as the quadratic polynomial of electric current,

The conduction voltage drop of IGBT is expressed as to the quadratic polynomial of electric current:

u _CE＝a _c+b _ci+c _ci ²；

The conduction voltage drop of diode is expressed as to the quadratic polynomial of electric current:

u _CE=a _f+b _fi+c _fi ²；

By the switch energy loss value E of IGBT _tswbe expressed as the quadratic polynomial of electric current:

E _Tsw＝(a _swon+b _swoni+c _swoni ²)+(a _swoff+b _swoffi+c _swoffi ²)

By the switch energy loss value E of diode _tswbe expressed as the quadratic polynomial of electric current:

E _Tsw=a _D+b _Di+c _Di ²；

3) loss of calculating three-level voltage source converter,

Wherein, above-mentioned steps 3) by following concrete steps, undertaken:

A. analyze the conducting duty ratio that obtains each IGBT and diode component

When the state of single-phase brachium pontis changes between positive voltage and zero time, the duty ratio of IGBT VT, diode VD is D _pand D ₀+=1-D _p; The state of single-phase brachium pontis changes between negative voltage and zero

time, the duty ratio of VT and VD is D _nand D ₀-=1-D _n;

The on-state loss of b.IGBT and diode component calculates

Because diode clamp formula three-level converter structure is symmetrical, and each IGBT module of selecting is identical with clamping diode characteristic, therefore only needs the on-state loss P to VT1, VT2, VD3, VD4 and VD5 _vT1cond, P _vT2cond, P _vD3cond, P _vD4cond, P _vD5condcarry out analytical calculation;

Two IGBT of the upper brachium pontis of the phase that wherein VT1, VT2 are this voltage source converter, two fly-wheel diodes of the lower brachium pontis of this phase that VD3, VD4 are this voltage source converter, VD5 is clamping diode;

$\begin{array}{c}{P}_{\mathrm{VT}1\mathrm{cond}}=\frac{1}{2\mathrm{\π}}\underset{0}{\overset{\mathrm{\π}-\mathrm{\θ}}{\∫}}{u}_{\mathrm{CE}}\×i\×D_P\mathrm{d\α}\\ =\frac{1}{2\mathrm{\π}}\underset{0}{\overset{\mathrm{\π}-\mathrm{\θ}}{\∫}}(a_c+b_{c}I\sin \mathrm{\α}+c_c{I}^2{\sin }^2\mathrm{\α})\\ \×I\sin \mathrm{\α}\×D_P\mathrm{d\α}\end{array}$

$\begin{array}{c}{P}_{\mathrm{VT}2\mathrm{cond}}=\frac{1}{2\mathrm{\π}}\underset{0}{\overset{\mathrm{\π}-\mathrm{\θ}}{\∫}}i(a_c+b_{c}i+c_c{i}^2)\×1\mathrm{d\α}+\\ \frac{1}{2\mathrm{\π}}\underset{\mathrm{\π}-\mathrm{\θ}}{\overset{\mathrm{\π}}{\∫}}i(a_c+b_{c}i+c_c{i}^2)(1-D_N)\mathrm{d\α}\end{array}$

$\begin{array}{c}{P}_{\mathrm{VD}3\mathrm{cond}}=P_{\mathrm{VD}4\mathrm{cond}}\\ =\frac{1}{2\mathrm{\π}}\underset{\mathrm{\π}-\mathrm{\θ}}{\overset{\mathrm{\π}}{\∫}}i(a_f+b_{f}i+c_f{i}^2)D_N\mathrm{d\α}\end{array}$

$\begin{array}{c}{P}_{\mathrm{VD}5\mathrm{cond}}=\frac{1}{2\mathrm{\π}}\underset{0}{\overset{\mathrm{\π}-\mathrm{\θ}}{\∫}}i(a_{f5}+b_{f5}i+c_{f5}{i}^2)(1-D_P)\mathrm{d\α}\\ +\frac{1}{2\mathrm{\π}}\underset{\mathrm{\π}-\mathrm{\θ}}{\overset{\mathrm{\π}}{\∫}}i(a_{f5}+b_{f5}i+c_{f5}{i}^2)(1-D_N)\mathrm{d\α}\end{array}$

The switching loss of c.IGBT and diode component is calculated

The computing formula of switching loss is

$P_{\mathrm{Tsw}}=\frac{1}{T_o}{\∫\mathrm{dE}}_{\mathrm{Tsw}}$

T in formula _o-power frequency period, f _s-switching frequency; E _tswfor at a certain temperature, the switch energy loss value in IGBT databook;

Can obtain thus the switching loss P of VT1 _t1sw, the reverse recovery loss P of VD5 _d5rec, the switching loss P of VT2 _t2sw, the reverse recovery loss P of VD4 _d4rec;

$\begin{array}{c}{P}_{T1\mathrm{sw}}=\frac{f_s}{2\mathrm{\π}}[\underset{0}{\overset{\mathrm{\π}-\mathrm{\θ}}{\∫}}(a_{\mathrm{swon}}+b_{\mathrm{swon}}i+c_{\mathrm{swon}}{i}^2)\mathrm{d\α}\\ +\underset{0}{\overset{\mathrm{\π}-\mathrm{\θ}}{\∫}}(a_{\mathrm{swoff}}+b_{\mathrm{swoff}}i+c_{\mathrm{swoff}}{i}^2)\mathrm{d\α}]\end{array}$

$P_{D5\mathrm{rec}}=\frac{f_s}{2\mathrm{\π}}\underset{0}{\overset{\mathrm{\π}-\mathrm{\θ}}{\∫}}(a_{D5}+b_{D5}i+c_{D5}{i}^2)\mathrm{d\α}$

$p_{T2\mathrm{sw}}=\frac{f_s}{2\mathrm{\π}}[\underset{\mathrm{\π}-\mathrm{\θ}}{\overset{\mathrm{\π}}{\∫}}(a_{\mathrm{swon}}+b_{\mathrm{swon}}+c_{\mathrm{swon}}{i}^2)\mathrm{d\α}+\underset{\mathrm{\π}-\mathrm{\θ}}{\overset{\mathrm{\π}}{\∫}}(a_{\mathrm{swoff}}+b_{\mathrm{swoff}}i+c_{\mathrm{swoff}}{i}^2)\mathrm{d\α}]$

$P_{D4\mathrm{rec}}=\frac{f_s}{2\mathrm{\π}}\underset{\mathrm{\π}-\mathrm{\θ}}{\overset{\mathrm{\π}}{\∫}}(a_{D4}+b_{D4}i+c_{D4}{i}^2)\mathrm{d\α}.$

2. diode clamp formula three-level voltage source converter loss analysis method according to claim 1, is characterized in that above-mentioned voltage source converter ac-side current is sinusoidal waveform, and DC capacitor voltage is balance.

Images