CN104849560A - Method for estimating differential mode interference noise impedance of equipment - Google Patents

Abstract

The invention discloses a method for measuring and estimating differential mode interference noise impedance through insertion loss. According to the method, a known impedance amplitude element is inserted into a circuit to measure voltage before and after the element is inserted so as to obtain the insertion loss value of the element. A noise source impedance amplitude range is obtained by drawing an impedance plane graph. According to the method, the operation is simple and easy, the experimental condition is simple, and the result precision is relatively high. The impedance value estimated by the estimation method is compared with a measured value of a laboratory, and the compared result indicates that the estimation range precision is high. Moreover, the estimation method also can be suitable for a system with unknown impedance, the impedance value estimated by the method is beneficial to later-stage filter parameter design, and the results also can provide effective data for an electromagnetic interference protective problem.

Description

The evaluation method of the differential mode interference noise resistance of equipment

(1) technical field

What the present invention relates to is the evaluation method of differential mode internal impedance in various motor driven systems, design due to wave filter needs the size knowing noise source impedance, for power converter selects suitable filter topologies to provide basis, belong to suppression and the design field of power electronics electromagnetic interference (EMI).

(2) background technology

Differential mode interference is the common and larger interference of impact of in electronic electric equipment.With interference another kind of in equipment---compared with common mode interference, differential mode interference is more difficult to remove and have impact to load.The method of suppression differential mode interference comparatively common at present adds passive filter, and select suitable wave filter prerequisite to be the differential mode source impedance that can obtain noise source.

Known by document and patent retrieval, at the beginning large quantity research has been done to differential mode interference characteristic both at home and abroad.Meng Jin, Ma Weiming, Zhang Lei etc. point out to be with the differential mode interference of the Switching Power Supply electrical network side of rectifier bridge input stage to there are two kinds of components: the essential differential mode interference component that rectifier bridge conduction period produces and the mixing jamming pattern component that rectifier bridge blocking interval produces.From the conclusion of its research, differential mode interference source frequency spectrum enriches, very difficult by directly measuring the noise source impedance obtaining each pattern.

Mauricio Cespedes and the measuring method of Jian Sun to three-phase circuit impedance of Rensselaer Polytech Inst of the U.S. (Rensselaer Polytechnic Institute) are summed up, and list the measuring method of common existing three-phase circuit impedance.The requirement of measuring process to equipment and personnel of cited method is comparatively strict, therefore, is not easy to realize.

Also document is had to relate to by the method be combined with theoretical analysis or modeling realizes carrying out differential mode interference analysis.The differential mode interference mechanism of Pei Xuejun to single-phase PWM full-bridge inverter of the Central China University of Science and Technology has carried out labor.The Liu Jia of Nanjing Aero-Space University establishes the Conduction Interference parameter model of full-bridge switch code converter main element, obtains differential mode interference current equivalence circuit model and the interference simulation model of full-bridge switch code converter Conduction Interference.But analysis modeling process need has abundant understanding to equipment inner structure, for the source impedance numerical value of electronics or electric product finished product, theoretical analysis modeling almost cannot realize.

Therefore, obtained by simple and easy method or estimate that differential mode noise source impedance is significant.

(3) summary of the invention

The present invention, with solving the unobtainable problem of differential mode noise source impedance, is mainly used in providing the amplitude range of differential mode noise source impedance in noise.Differential mode interference source forms loop by the inductive resistance of system line, and the common mode differential-mode current of its three-phase inverter drive system flows to as shown in Figure 1.Because noise source frequency spectrum is generally abundanter, make the calculated amount of differential mode noise source impedance heavy.On the other hand, compared with the impedance of acquisition common-mode sources, the differential mode noise loop of practical problems is often positioned at internal system, and comparatively complicated.In view of above 2 problems, in practical problems, differential mode noise source impedance generally cannot obtain.The present invention mainly through estimating differential mode source impedance amplitude, to solve the impact that brings to filter design problem of noise source impedance the unknown.Detailed process is as follows:

1. before measuring insertion element, noise source produces the amplitude U of voltage in load _lDM0, obtain the amplitude spectrum density of its frequency domain.Noise source is directly connected with LISN, Z on voltage magnitude and pull-up resistor _lDMdividing potential drop.Z _lDMfor loaded impedance, here by two 50 Ω resistance in series of LISN side, its value is 100 Ω.

2. insert resistance value well known elements Z _shunt, this element impedance value is generally obtained by electric impedance analyzer.This element inserted mode has series connection with in parallel, and cascade process theory calculate is simple, but larger to differential mode problem range of results error, parallel method range of results is more accurate, and be connected in parallel in circuit structure and be easy to insert, therefore to differential mode noise source impedance process, insert well known elements with parallel way.Again measure the partial pressure value U of resistance on LISN _lDMfrequency domain amplitude spectrum.The circuit diagram of insertion element as shown in Figure 2.

3. enroll relative program by according to voltage magnitude spectrum before and after the insertion element measured, for each single frequency, according to insertion loss principle, insertion loss is defined as ${\mathrm{IL}}_{\mathrm{DM}}=20\lg \left|\frac{U_{\mathrm{LDM}0}\left(\mathrm{\ω}\right)}{U_{\mathrm{LDM}}\left(\mathrm{\ω}\right)}\right|.$

4. by load impedance value recording program.Program operation process describes by complex impedance plane figure, wherein its complex impedance point of correspondence-Z of loaded impedance _lDMi.e. (-Re (Z _lDM) ,-Im (Z _lDM)) if Z _lDMfor loaded impedance is served as by the LISN resistance in the 1st step, then its value is (100+j0) Ω.Impedance Z _lDMmodulus value can be used as the coordinate unit length of planimetric map coordinate.Impedance plane diagram schematic diagram as shown in Figure 3.

5. working procedure obtains the scope of important estimator with the insertion loss value of step 3, the radius upper limit K namely in impedance estimation process _awith lower limit K _b. $K_A=\frac{\left(\right|A_{\mathrm{DM}}|+1)\left|Z_{\mathrm{shunt}}\right|}{\left|Z_{\mathrm{LDM}}\right|},K_B=\frac{\left(\right|A_{\mathrm{DM}}|-1)\left|Z_{\mathrm{shunt}}\right|}{\left|Z_{\mathrm{LDM}}\right|}.$

6. realize the estimation of noise source impedance magnitude in a program, represent that the detailed process of this step is as follows intuitively at negative impedance planimetric map

By K _awith K _bin with 1 do difference get reciprocal after value the greater as effective radius multiple R.With effective radius multiple R and coordinate unit length | Z _lDM| product as radius, do circle with loaded impedance.Whole points that circumference marks comprise the source impedance value point of noise source impedance, therefore in mapping, and circumference is the maxima and minima of the noise source impedance amplitude of estimation to the distance solstics of initial point and closest approach.

7., by the numerical value that the above-mentioned mapping of each point obtains, obtain maximal value curve and the minimum value curve of all frequency noise source impedance amplitude of whole measurement frequency domain, estimated range is defined by two curves.

(4) accompanying drawing explanation

The induction motor system that Fig. 1 three-phase inverter drives

The circuit model that Fig. 2 differential mode noise source impedance is measured

Common-mode noise source impedance amplitude when Fig. 3 load is purely resistive

The impedance operator of Fig. 4 electric capacity

Fig. 5 accesses the differential mode voltage before electric capacity

Fig. 6 accesses the differential mode voltage after electric capacity

Fig. 7 Differential Mode insertion loss

The maximal value of Fig. 8 differential mode noise source impedance and minimum value

(5) embodiment

With by 1 Ω resistance and 0.1 μ F capacitances in series Z _shuntmaking parallel impedance device is that example elaborates to the present invention.

To impedance Z _shuntin capacitive part, its impedance magnitude is obtained by electric impedance analyzer measurement with frequency change relation, as shown in Figure 4.

Measure the voltage U before and after access electric capacity _lDM0with U _lDMamplitude.U _lDM0with U _lDMamplitude see Fig. 5 and Fig. 6 respectively with frequency change relation.

According to measuring numerical value, draw insertion loss IL according to the 3rd step _dM, Differential Mode insertion loss value is shown in Fig. 7 with the variation relation of frequency.

Obtain noise source impedance ranges according to the mapping of step 4-step 7, more each band limits combination is obtained the estimated range of whole frequency domain.

Here the measured value that experiment test obtains differential mode noise source impedance is given by.Fig. 8 describes differential mode noise source impedance estimated range and its actual value relation.Can find out, actual value is between maxima and minima, and difference between maxima and minima is less, shows that estimation accuracy of the present invention is higher, can be applied in the occasion that differential mode noise source impedance is difficult to measure, have very large actual value.

Claims (4)

1. the evaluation method of electronic system differential mode interference noise resistance, significant and be not easy to the feature measured for System level gray correlation mode noise source impedance, the present invention proposes a kind of effective differential mode noise source impedance amplitude range evaluation method.

2. requirement according to claim 1, the present invention obtains the insertion loss of circuit according to measuring the load voltage values inserted before and after impedance well known elements.

3. on the basis of right 2, on impedance plane diagram, mark loaded impedance, and using loaded impedance as the center of circle, radius of circle is obtained by measured insertion loss value.

4. circumferentially comprise the source impedance value point of noise source impedance, circumference is defined as the maxima and minima of the noise source impedance amplitude of estimation to the distance solstics of initial point and closest approach.