CN103595243B - Be applicable to the method suppressing common mode electromagnetic interference in wind-driven generator drive system - Google Patents

Abstract

The invention discloses a kind of method being applicable to suppress common mode electromagnetic interference in wind-driven generator drive system, parasitic capacitance during switching tube action between switching tube and radiator produces interference to ground leakage current i _l, interference to ground leakage current i _lflow to the earth terminal of radiator; The voltage change signal du/dt that switching tube action produces accesses the input of inverter, by the acting in opposition of inverter, inverter output exports a voltage change signal that amplitude is equal, phase place is contrary, and this voltage change signal is by the isolating transformer for preventing disturbance current from refluxing and building-out capacitor C _p, form offset current-i _l, entered the earth terminal of radiator by wire, interference to ground leakage current i _lwith offset current-i _lamplitude is equal, phase place is contrary, thus cancels out each other, and inhibits interference to ground leakage conduction common mode disturbances.The present invention is in the reduction complexity of system and the basis of cost, and effective common mode disturbances that must inhibit in drive system, improves stability and the Electro Magnetic Compatibility of system.

Description

Be applicable to the method suppressing common mode electromagnetic interference in wind-driven generator drive system

Technical field

The present invention relates to a kind of method suppressing common mode disturbances, particularly relate to a kind of method being applicable to suppress common mode electromagnetic interference in wind-driven generator drive system.

Background technology

PWM motor driven systems is widely adopted at home in recent years, inverter for PWM motor driven systems also launches the research work that whole system affects thereupon, the research wherein relating to the electromagnetic interference problem of PWM motor driven systems and inverter is but also still perfect not, Zhejiang University conducts in-depth research with regard to the mechanism of production of the Conducted Electromagnetic Interference of Buck circuit and braking measure thereof, and propose dynamic node potentiometer balanced methods for magnesium, but this measure be not suitable for the suppression of the electromagnetic interference of drive system.

The electromagnetic compatibility problem of current various countries to motor driven systems all takes much count of, successively expand in theory with the correlative study work in engineering.Although propose a lot of suppressing method to conduction common mode disturbances, but the braking measure proposed for the interference that motor driven systems exists all also exists some limitation, if these method improper uses, not only can not reach and suppress the object of electromagnetic interference, on the contrary may the electromagnetic interference of heavy system.Existing braking measure all making system configuration become complicated in varying degrees, add cost, and most of research work being all the common-mode voltage how reducing system, and have ignored from locally improving, realizing the direct suppression to common mode disturbances leakage current.

In motor driven systems, damage because of overheated to prevent power switch pipe, usually itself and radiator are installed together, in order to prevent their open circuits, heat conductive insulating medium is adopted to isolate between the metallic plate level of each power tube and radiator, result between power tube and radiator and form parasitic capacitance, from this coupling path, radiator is connected with the earth by the casing of motor, parasitic capacitance will provide a low-impedance coupling circuit over the ground for system leakage current, the leakage current of system will be flowed to publicly through motor case by radiator, cause common mode disturbances, if radiator is not connected to the ground, although cut off the propagation circuit of system leakage current, hf interference current will be coupled to spreader surface, makes it become the antenna of a voltage drive, thus has just increased the weight of inverter Radiative EMI.In general, radiator is all connected with motor case, so the parasitic capacitance between power tube and radiator is the main cause that system produces common mode disturbances.

Although the parasitic capacitance between power tube and radiator can be reduced by the size reducing radiator, increase the impedance of coupling circuit, thus reduction Conducted Electromagnetic Interference, but the radiating efficiency of radiator also have dropped simultaneously thereupon, be unfavorable for the normal work of whole system, so it is impracticable for reducing Conducted Electromagnetic Interference by reduction heat sink size.At present, most research work is all in radiated interference problem, and realizes not paid close attention to the suppression of Conducted Electromagnetic Interference by common mode disturbances leakage compensated principle.

Summary of the invention

For solving the problem, the invention provides a kind of applied current and compensating the method suppressing motor driven systems conduction common mode electromagnetic interference from local.

The mentality of designing of inventor comes from the following analysis of inventor:

Damage because of overheated to prevent power switch pipe, usually itself and radiator are installed together, in order to prevent their short circuits, between the metal polar plate of each power tube and radiator, adopting heat conductive insulating medium to isolate, just defining a parasitic capacitance between them like this.Can acute variation be there is in power tube voltage when switch motion, the drastic change of voltage will form common-mode interference current by this parasitic capacitance, this electric current flows to the earth through radiator, gets back to DC side, then flow to driver by DC bus by linear impedance stabilization network.

Fourier's expression formula of the three-phase phase voltage that driver exports is shown below:

U in formula _a, U _b, U _c-be respectively driver A phase, phase voltage V that B phase, C phase export; ω ₁, ω _s-be respectively angular frequency and the carrier angular frequencies rad/s of modulating wave; U _dc-DC bus-bar voltage V; A-modulation depth.

Section 1 in above formula is first-harmonic composition, and the fundamental voltage amplitude exporting phase voltage is aU _dc/ 2, Section 2 is harmonic components.Substitution formula U _cm=(U _a+ U _b+ U _cin)/3, utilize Bessel function can obtain Fourier's expression formula of common-mode voltage, be shown below:

$\left\{\begin{array}{c}{u}_{\mathrm{cm}}=\underset{n=1}{\overset{\∞}{\mathrm{\Σ}}}{(-1)}^{(n-1)/2}\frac{U_{\mathrm{dc}}}{2}\left(\frac{4}{\mathrm{n\π}}\right)\left\{J_0\left(\frac{\mathrm{an\π}}{2}\right)\cos \left({\mathrm{n\ω}}_{s}t\right)\right\}+\\ 3\underset{n=1}{\overset{\∞}{\mathrm{\Σ}}}{J}_k\left(\frac{\mathrm{an\π}}{2}\right)[\cos ({\mathrm{k\ω}}_1+{\mathrm{n\ω}}_s)t+\cos ({\mathrm{k\ω}}_1-{\mathrm{n\ω}}_s)t]\}\\ n=\mathrm{1,3,5}...,k=6l,l=\mathrm{1,2,3},...\\ u_{\mathrm{cm}}=3\underset{n=2}{\overset{\∞}{\mathrm{\Σ}}}{(-1)}^{n/2}\frac{U_{\mathrm{dc}}}{2}\left(\frac{4}{\mathrm{n\π}}\right)\left\{J_k\left(\frac{\mathrm{an\π}}{2}\right)\right[\sin ({\mathrm{k\ω}}_1+{\mathrm{n\ω}}_s)t+\sin ({\mathrm{k\ω}}_1-{\mathrm{n\ω}}_s)t\left]\right\}\\ n=\mathrm{2,4,6}...,k=6l-3,l=\mathrm{1,2,3},...\end{array}\right.$

U in formula _cm---the common-mode voltage (V) that driver exports; J _k---k rank Bessel function.

Can be known by above formula:

(1) amplitude of first-harmonic composition is 0, and not containing frequency in common-mode voltage is the composition of switching frequency.

(2) harmonic components:

When carrier frequency is ω _sodd-multiple time, containing amplitude be harmonic components; When even-multiple not containing harmonic components.When angular frequency is (k ω ₁± n ω _s) time there is humorous wave component, amplitude is:

$\frac{U_{\mathrm{dc}}}{2}\frac{12}{\mathrm{n\π}}{J}_k\left(\frac{\mathrm{an\π}}{2}\right),\left\{\begin{array}{c}n=\mathrm{1,3,5}...,k=6l\\ n=\mathrm{2,4,6}...,k=6l-3(l=\mathrm{1,2,3}...)\end{array}\right.$

Harmonic components is with frequency n ω _scentered by, side frequency ± k ω ₁distribution both sides, amplitude is at central point n ω _sbilateral symmetry decays, and constantly reduces along with the increase of carrier frequency frequency.

From above-mentioned mathematics model analysis, the harmonic components of the common mode disturbance voltage produced by drive system is maximum at the amplitude of carrier frequency, and this frequency characteristic is conducive to the suppression realizing common mode disturbances.

Analyze based on this, inventor provide a kind of method being applicable to suppress common mode electromagnetic interference in wind-driven generator drive system, its technical scheme is as follows:

1, by switching tube and radiator abstract be two metal polar plates of plate condenser, utilize the capacitance of the capacitor parasitics formed between following formulae discovery switching tube and radiator:

$C_0=\frac{{\mathrm{\ϵ}}_0{\mathrm{\ϵ}}_{r}A}{d}$

In formula: C ₀---parasitic capacitance (F); A---metal polar plate area (m ²); D---mica sheet thickness (m); ε ₀---permittivity of vacuum; ε _r---relative dielectric constant;

2, the capacitance that LCR tester obtains the capacitor parasitics formed between switching tube and radiator is applied;

3, by the calculated value comparison of the capacitance of capacitor parasitics in the measured value of the capacitance of the capacitor parasitics of LCR tester acquisition in step 2 and step 1;

Whether the capacitor parasitics that 4, in computational analysis step 2, LCR tester is measured is the parasitic coupling capacitance between switching tube and radiator, and the measured value of capacitance and the relative error of calculated value are:

If relative error is less than or equal to 7%, then defining the capacitor parasitics that LCR tester measures is parasitic coupling capacitance between switching tube and radiator;

5, on switching tube, draw the input of wire access inverter, inverter is connected with isolating transformer and building-out capacitor Cp, and series circuit is connected to radiator through wire, the earth terminal ground connection of radiator; The capacitance of described building-out capacitor Cp is the capacitance of the capacitor parasitics formed between the switching tube of application LCR tester acquisition and radiator;

During use, parasitic capacitance during switching tube action between switching tube and radiator produces interference to ground leakage current i _l, interference to ground leakage current i _lflow to the earth terminal of radiator; The voltage change signal du/dt that switching tube action produces accesses the input of inverter, by the acting in opposition of inverter, inverter output exports a voltage change signal that amplitude is equal, phase place is contrary, this voltage change signal, by the isolating transformer for preventing disturbance current from refluxing and building-out capacitor Cp, forms offset current-i _l, entered the earth terminal of radiator by wire, interference to ground leakage current i _lwith offset current-i _lamplitude is equal, phase place is contrary, thus cancels out each other, and inhibits interference to ground leakage conduction common mode disturbances.

Beneficial effect performance of the present invention is as follows:

1, the present invention is by reducing the electromagnetic interference of drive system, can improve useful life that is electric in whole system, electronic equipment components and parts.

2, the present invention is in the reduction complexity of system and the basis of cost, and effective common mode disturbances that must inhibit in drive system, improves stability and the Electro Magnetic Compatibility of system.

3, the invention process process is simple, is easy to operation, saves manpower.

Accompanying drawing explanation

Fig. 1 is common mode disturbances leakage compensated schematic diagram of the present invention;

Common-mode voltage frequency spectrum before Fig. 2 common mode disturbances leakage compensated;

Common-mode voltage frequency spectrum after Fig. 3 common mode disturbances leakage compensated.

Embodiment

In conjunction with the drawings and the specific embodiments the present invention is further described.

Embodiment

Be applicable to the method suppressing common mode electromagnetic interference in wind-driven generator drive system, its technical scheme is as follows:

1, by abstract to switching tube 1 and radiator 2 be two metal polar plates of plate condenser, make the area of two metal polar plates be 0.000225m ², mica sheet thickness is 0.00005m, utilizes the capacitance of the capacitor parasitics formed between following formulae discovery switching tube 1 and radiator 2:

$C_0=\frac{{\mathrm{\ϵ}}_0{\mathrm{\ϵ}}_{r}A}{d}=\frac{8.85\×5.5\×0.000225}{0.00005}=219.04\mathrm{pF};$

In formula: C ₀---parasitic capacitance (F); A---metal polar plate area (m ²); D---mica sheet thickness (m); ε ₀---permittivity of vacuum; ε _r---relative dielectric constant;

2, apply the capacitance that LCR tester obtains the capacitor parasitics formed between switching tube 1 and radiator 2, in the present embodiment, the measurement capacitance that LCR measuring instrument obtains is 205.76;

3, by the calculated value comparison of the capacitance of capacitor parasitics in the measured value of the capacitance of the capacitor parasitics of LCR tester acquisition in step 2 and step 1;

Whether the capacitor parasitics that 4, in computational analysis step 2, LCR tester is measured is the parasitic coupling capacitance between switching tube 1 and radiator 2, and the measured value of capacitance and the relative error of calculated value are:

Thus, defining the capacitor parasitics that LCR tester measures is parasitic coupling capacitance between switching tube 1 and radiator 2;

5, as described in Figure 1, switching tube 1 is drawn the input of wire access inverter 3, and inverter 3 is connected with isolating transformer 4 and building-out capacitor Cp5, and series circuit is connected to radiator 2 through wire, the earth terminal ground connection of radiator 2; The capacitance of described building-out capacitor Cp5 is the capacitance of the capacitor parasitics formed between the switching tube 1 of application LCR tester acquisition and radiator 2, i.e. C _p=205.76;

During use, parasitic capacitance during switching tube 1 action between switching tube 1 and radiator 2 produces interference to ground leakage current i _l, interference to ground leakage current i _lflow to the earth terminal of radiator 2; The voltage change signal du/dt that switching tube 1 action produces accesses the input of inverter 3, by the acting in opposition of inverter 3, inverter 3 output exports a voltage change signal that amplitude is equal, phase place is contrary, this voltage change signal, by the isolating transformer 4 for preventing disturbance current from refluxing and building-out capacitor Cp5, forms offset current-i _l, entered the earth terminal of radiator 2 by wire, interference to ground leakage current i _lwith offset current-i _lamplitude is equal, phase place is contrary, thus cancels out each other, and inhibits interference to ground leakage conduction common mode disturbances.

As shown in Figures 2 and 3, by Saber simulation software, simulation model is set up to whole drive system, the waveform of the voltage current waveform of emulation and actual measurement can contrast by the foundation of this simulation model, and the EMC analysis for whole system provides a good experiment porch.

Claims (1)

1. be applicable to the method suppressing common mode electromagnetic interference in wind-driven generator drive system, it is characterized in that comprising the following steps:

A, by abstract to switching tube (1) and radiator (2) be two metal polar plates of plate condenser, utilize the capacitance of the capacitor parasitics formed between following formulae discovery switching tube (1) and radiator (2):

$C_0=\frac{{\mathrm{\ϵ}}_0{\mathrm{\ϵ}}_{r}A}{d}$

In formula: C ₀---parasitic capacitance (F); A---metal polar plate area (m ²); D---mica sheet thickness (m); ε ₀---permittivity of vacuum; ε _r---relative dielectric constant;

B, application LCR tester obtain the capacitance of the capacitor parasitics formed between switching tube (1) and radiator (2);

The calculated value comparison of the capacitance of capacitor parasitics in c, the measured value of capacitance of capacitor parasitics that LCR tester in step b is obtained and step a;

In d, computational analysis step b, whether the capacitance of the capacitor parasitics that LCR tester is measured is the capacitance of the parasitic coupling capacitance between switching tube (1) and radiator (2), and the measured value of capacitance and the relative error of calculated value are:

If relative error is less than or equal to 7%, then the capacitance defining the capacitor parasitics that LCR tester is measured is the capacitance of the parasitic coupling capacitance between switching tube (1) and radiator (2);

The input of e, extraction wire access inverter (3) on switching tube (1), inverter (3) is connected with isolating transformer (4) and building-out capacitor Cp (5), series circuit is connected to radiator (2) through wire, the earth terminal ground connection of radiator (2); The capacitance of described building-out capacitor Cp (5) is the capacitance of the capacitor parasitics formed between the switching tube (1) of application LCR tester acquisition and radiator (2);

Parasitic capacitance when f, switching tube action between switching tube and radiator produces interference to ground leakage current i _l, interference to ground leakage current i _lflow to the earth terminal of radiator; The voltage change signal du/dt that switching tube action produces accesses the input of inverter, by the acting in opposition of inverter, inverter output exports a voltage change signal that amplitude is equal, phase place is contrary, this voltage change signal, by the isolating transformer for preventing disturbance current from refluxing and building-out capacitor Cp, forms offset current-i _l, entered the earth terminal of radiator by wire, interference to ground leakage current i _lwith offset current-i _lamplitude is equal, phase place is contrary, thus cancels out each other, and inhibits interference to ground leakage conduction common mode disturbances.