CN103091558A - Drawing circuit for resistance in photovoltaic grid-connected inverter direct current side noise source and method - Google Patents

Abstract

The invention discloses a drawing circuit for resistance in photovoltaic grid-connected inverter direct current side noise source and a method. The drawing circuit comprises a direct current voltage source, a signal source, a current probe, a spectrum analyzer and a grid-connected inverter. A negative pole on the direct current side of the grid-connected inverter is connected with the signal source through a radio frequency cable. The signal source is connected to a negative pole of the direct current voltage source. A positive pole of the direct current voltage source is connected with a positive pole on the direct current side of the grid-connected inverter through a wire. Single current probe is arranged on the wire. The single current probe is connected to the spectrum analyzer. According to the fact that high-frequency noise signal voltage in a circuit detection circuit is drawn, resistance of the photovoltaic grid-connected inverter direct current side noise source and in a conduction electro-magnetic interference (EMI) frequency range (150KHz to 30 MHz) can be effectively drawn through the fact that high-frequency signal output frequencies of the signal power source are changed one by one. According to the drawing circuit for the resistance in the photovoltaic grid-connected inverter direct current side noise source, the conduction EMI noise characteristic analysis on the direct current side of the photovoltaic grid-connected inverter and design of an EMI filter are guided, and an effective theory solution is provided for solving of the problems of the conductive EMI on the direct current side of the photovoltaic grid-connected inverter.

Description

Extraction circuit and the method for photovoltaic combining inverter DC side noise source internal impedance

Technical field

The present invention relates to a kind of extraction circuit and method of photovoltaic combining inverter DC side noise source internal impedance, for Analysis on Mechanism and the inhibition of Conducted Electromagnetic Interference (EMI) noise of the DC power-supply system in the power electronics application system provides theory support, belong to new forms of energy and electromagnetic compatibility technology field.

Background technology

Along with the day by day in short supply of traditional energy and the problem of environmental pollution that causes day by day serious, improve energy structure and development new forms of energy, improve the strategic target that the new forms of energy quality of power supply has risen to China's energy development.Simultaneously, fast development along with Power Electronic Technique, photovoltaic generation and interconnection technology thereof are widely applied, but a large amount of power electronic devices that adopt of photovoltaic combining inverter will cause very serious emc issue to electrical network, and the high dv/dt, the di/dt that wherein exist in the DC converting of combining inverter part are one of reasons that causes system's Conducted Electromagnetic Interference problem.In addition, the Conducted EMI problem that makes DC side of selecting of the chip of high frequency, large scale integrated circuit and components and parts becomes increasingly conspicuous, yet in order effectively to solve the Conducted EMI problem of DC side, designing efficient Conducted EMI wave filter is one of effective method, but during design Conducted EMI wave filter, must know the noise source internal resistance, so just can make the Conducted EMI wave filter reach the optimum filtering performance.Therefore carrying out for the photovoltaic combining inverter DC side method research that the noise source internal impedance extracts is absolutely necessary.

At present electromagnetic compatibility standard is the compulsory standard of produce market access, and no matter electric and electronic product at home or international marketing, all must reach corresponding EMC standard and just can sell on market.therefore, the inhibition of electromagnetic interference (EMI) (EMI) noise emission is an essential major issue of considering in electric and electronic device design and manufacture process, at present the Conducted EMI squelch of DC power-supply system adopted empirical value method design Conducted EMI wave filter usually, because the empirical value method does not consider matching problem between noise source impedance and loaded impedance, thereby the Conducted EMI wave filter of designing often is difficult to have filtering performance preferably, the main cause that causes this situation to occur is to extract for the noise source internal impedance of photovoltaic combining inverter DC side there is no a kind of system, effective method, thereby can't carry out the assessment of impedance matching property.

Summary of the invention

Technical matters to be solved by this invention is to overcome the defective that prior art exists, and proposes a kind of photovoltaic combining inverter DC side noise source internal impedance extracting method based on single current probe.The method can effectively be extracted photovoltaic combining inverter DC side noise source internal impedance, instruct the Conducted EMI Analysis of Noise Properties of photovoltaic combining inverter DC side and the design of electromagnetic interface filter, for the Conducted EMI solution of problem of photovoltaic combining inverter DC side provides effective theoretical solution.

Photovoltaic combining inverter DC side Conducted EMI noise is one of major parameter of check DC power-supply system Electro Magnetic Compatibility.In order to make DC side have Electro Magnetic Compatibility preferably, must the Conducted EMI noise of its generation be suppressed, and the Conducted EMI wave filter is the Main Means of realizing the Conducted EMI squelch, in order to design efficient electromagnetic interface filter, must know the noise source internal impedance of photovoltaic combining inverter DC side.The double-current probe method is to extract comparatively effectively one of means of noise source internal impedance, but experimental cost is higher, needs two current probes.For reducing experimental cost, the present invention proposes the single current probe method based on the photovoltaic combining inverter DC side, the concrete technical scheme of the circuit of employing is as follows:

The extraction circuit of photovoltaic combining inverter DC side noise source internal impedance, comprise direct voltage source, signal source, current probe, spectrum analyzer and combining inverter, wherein, the negative pole of combining inverter DC side is connected with signal source by RF cable, and described signal source is connected to the negative pole of direct voltage source; The positive pole of described direct voltage source is connected by the positive pole of wire with the combining inverter DC side, and described wire is provided with the single current probe; Described single current probe is connected to spectrum analyzer.

Described signal source comprises signal generator, the internal impedance of signal generator output port is 50 Ω, therefore the output signal of the signal generator radio-frequency voltage source that to be equivalent to an internal impedance be 50 Ω, connect respectively capacitance of the two ends of this voltage source forms series circuit, and described series circuit is in parallel with a bypass resistance again.

The present invention utilizes the extracting method of described circuit, comprises the steps:

(1) direct voltage source and signal source are connected to the DC side of combining inverter;

(2) substitute the combining inverter place in circuit with normal impedance, the output signal frequency f in conditioning signal source ₀, then access current probe and spectrum analyzer, the HF noise signal voltage U in metering circuit _t1

(3) with the normal impedance short circuit, give the work of circuit normal power supply, utilize the HF noise signal voltage U in the current probe metering circuit _t2

(4) with combining inverter alternate standard impedance place in circuit, when inverter works, utilize the HF noise signal voltage U in the current probe metering circuit _t3

(5) magnitude of voltage that obtains according to step (2), (3) and (4), calculating noise source internal impedance is:

$Z_x=\frac{{R_{\mathrm{std}}{U}_t|}_{Z_x=R_{\mathrm{std}}}}{{U_t|}_{Z_x=\mathrm{SMPS}}}-\frac{{U_t{R}_{\mathrm{std}}|}_{Z_x=R_{\mathrm{std}}}}{{U_t|}_{Z_x=0}}$

Wherein, R _stdBe normal impedance, U _t1For normal impedance substitutes HF noise signal voltage in the circuit that lower current probe records, U _t2HF noise signal voltage in the circuit that records for current probe under the normal impedance short-circuit conditions, U _t3HF noise signal voltage in the circuit that when working for the combining inverter place in circuit, current probe records;

(6) change one by one the high-frequency signal output frequency f of signal source ₀, f ₀=0.15,1,2 ..., N ..., 30MHz, wherein N is integer, repeating step (2) is measured magnitude of voltage and noise source internal impedance under each signal frequency to (5).

Extraction for photovoltaic combining inverter DC side noise source internal impedance, the present invention has designed effective extraction circuit, and concrete internal impedance extracting method proposed, for diagnosis, the analysis and inhibition of the DC side Conducted EMI noise of photovoltaic combining inverter provides effective theory support, and have very large application in practice and be worth, provide effective reference for improving photovoltaic combining inverter DC side Conducted Electromagnetic compatibility feature.

Description of drawings

Fig. 1 is the schematic diagram that adopts single current probe method that DC power-supply system noise source internal impedance is extracted.

Fig. 2 is the equivalent circuit diagram of Fig. 1 impedance extraction principle.

Fig. 3 is that embodiment of the present invention combining inverter DC side noise source internal impedance is extracted schematic diagram.

Fig. 4 is that photovoltaic combining inverter DC side noise source internal impedance is extracted the experimental verification platform, is used for verifying the validity of noise source internal impedance extracting method proposed by the invention.

Fig. 5 is radiofrequency signal injection circuit pictorial diagram, primary injection for radiofrequency signal.

Fig. 6 is that photovoltaic combining inverter DC side noise source internal impedance is extracted result.

Embodiment

Below in conjunction with instantiation, the inventive method is described in further detail.

Be illustrated in figure 1 as the noise source internal impedance extraction schematic diagram based on the DC power-supply system of single current probe, comprising signal source, current probe, frequency spectrograph and impedance to be measured, wherein signal source is the high frequency Injection Signal, current probe is that high-frequency signal detects use, and the cable equiva lent impedance is resistance, appearance, the sense characterisitic parameter of cable self.Radiofrequency signal is provided in experimental system due to signal generator, its power is less, withstand voltage also lower, damage for fear of its high pressure that is subject to tested DC power-supply system, need to be at its signal output part series connection capacitance, according to the electromagnetic compatibility standard regulation, the conventionally test frequency range of conducted electromagnetic interference noise is 150KHz-30MHz, therefore suitable as long as capacitance appearance value size is chosen, can guarantee that just the output signal of signal generator is effectively transmitted.Simultaneously for guarantee system under test (SUT) direct current supply effectively the signal of power supply and signal generator output effectively enter system under test (SUT), for impedance extraction, need bypass resistance of parallel connection on the primary circuit basis, it is definite that resistance sizes is tested needs according to impedance extraction.

Be illustrated in figure 2 as the equivalent circuit diagram of Fig. 1 impedance extraction principle, wherein U _MBe the output voltage of signal source, Z _nBe the internal impedance of signal source, C _g1And C _g2Be 0.1uF capacitance, R _pBe 10 Ω bypass resistances, Z _tBe current probe mutual inductive impedance on the line, Z _cBe cable impedance.

Signal source U _MProduce in the line circuit I during normal operation _w, according to the equivalent electrical circuit of Fig. 2, can obtain four equations of this circuit:

$\left\{\begin{array}{c}{u}_{aa\&prime;}=I_w(Z_t+Z_c+Z_x)\\ I_p=u_{a{a}^{\&prime;}}/R_p\\ I_M=I_w-I_p\\ U_M=I_M(Z_n+1/\mathrm{<figure-callout\; id="1"\; label="jw\; C\; g"\; filenames="HDA00002754628000032.png"\; state="\{\{state\}\}">jw</figure-callout>}{C}_g{1}_{}+1/\mathrm{jw}{C}_{g2})+u_{aa\&prime;}\end{array}\right.---\left(1\right)$

I wherein _pFor flowing through the electric current of bypass resistance branch road, I _MBe signal source branch road total current, can get according to equation (1):

U _M=(I _w-I _w(Z _t+Z _c+Z _x)/R _p)(Z _n+1/jwC _g1+1/jwC _g2)+I _w(Z _t+Z _c+Z _x) （2）=I _w[(1-(Z _t+Z _c+Z _x)/R _p)(Z _n+1jwC _g1+1/jwC _g2)+Z _t+Z _c+Z _x]

Owing to removing Z in formula _xOther outer impedances are all definite value, therefore equation (2) can be reduced to:

$U_M=I_w\left\{\begin{array}{c}(Z_n+1/\mathrm{<figure-callout\; id="1"\; label="jw\; C\; g"\; filenames="HDA00002754628000032.png"\; state="\{\{state\}\}">jw</figure-callout>}{C}_g{1}_{}+1/\mathrm{jw}{C}_{g2}+Z_t+Z_c-\frac{(Z_t+Z_c)(Z_n+1/\mathrm{<figure-callout\; id="1"\; label="jw\; C\; g"\; filenames="HDA00002754628000032.png"\; state="\{\{state\}\}">jw</figure-callout>}{C}_g{1}_{}+1/\mathrm{jw}{C}_{g2})}{R_p})\\ -(\frac{(Z_n+1/\mathrm{<figure-callout\; id="1"\; label="jw\; C\; g"\; filenames="HDA00002754628000032.png"\; state="\{\{state\}\}">jw</figure-callout>}{C}_g{1}_{}+1/\mathrm{jw}{C}_{g2})}{R_p}+1)Z_x\end{array}\right\}---\left(3\right)$

$=I_w({Z_{\mathrm{in}}}^{\&prime;}+K_z{Z}_x)$

Wherein:

${Z_{\mathrm{in}}}^{\&prime;}=Z_n+1/\mathrm{<figure-callout\; id="1"\; label="jw\; C\; g"\; filenames="HDA00002754628000032.png"\; state="\{\{state\}\}">jw</figure-callout>}{C}_g{1}_{}+1/\mathrm{jw}{C}_{g2}+Z_t+Z_c-\frac{(z_t+Z_c)(Z_n+1/\mathrm{<figure-callout\; id="1"\; label="jw\; C\; g"\; filenames="HDA00002754628000032.png"\; state="\{\{state\}\}">jw</figure-callout>}{C}_g{1}_{}+1/\mathrm{jw}{C}_{g2})}{R_p}$

$k_z=\frac{(Z_n+1/\mathrm{<figure-callout\; id="1"\; label="jw\; C\; g"\; filenames="HDA00002754628000032.png"\; state="\{\{state\}\}">jw</figure-callout>}{C}_g{1}_{}+1/\mathrm{jw}{C}_{g2})}{R_p}+1$

In case Z _n, C _g1, C _g2And R _pDetermine, K _ZBe the fixed value that can calculate.The expression formula that therefore, can obtain tested impedance is:

$Z_x=\frac{1}{K_z}(\frac{U_M}{I_w}-{Z_{\mathrm{in}}}^{\&prime;})=\frac{1}{K_z}(\frac{U_t}{I_w}\frac{U_M}{U_t}-{Z_{\mathrm{in}}}^{\&prime;})=\frac{1}{K_z}(\frac{U_M}{U_t}{Z}_{t^{\&prime;}}-{Z_{\mathrm{in}}}^{\&prime;})---\left(4\right)$

Can be calculated wherein Z _t’Be fixed value, and only with self relating to parameters that detects current probe.The output of holding signal source is constant, for given frequency, Z _t’U _MIt is a fixed value.With unknown impedance with a known measuring resistance R _stdSubstitute, and K _zR _stdZ _in',

$Z_{t^{\&prime;}}{U}_M={K_z{U}_t{Z}_x|}_{Z_x=R_{\mathrm{std}}}=K_z{U}_t{R}_{\mathrm{std}}---\left(5\right)$

With Z _xShort circuit can be surveyed impedance Z _in',

${Z_{\mathrm{in}}}^{\&prime;}={\frac{U_M}{U_t}{Z}_{t^{\&prime;}}|}_{Z_x=0}=\frac{{Z_{t^{\&prime;}}{U}_M|}_{Z_x=R_{\mathrm{std}}}}{{U_t|}_{Z_x=0}}=\frac{{K_z{U}_t{R}_{\mathrm{std}}|}_{Z_x=R_{\mathrm{std}}}}{{U_t|}_{Z_x=0}}---\left(6\right)$

When measuring photovoltaic combining inverter DC side noise source internal impedance, its test philosophy figure as shown in Figure 3, V wherein _DBe dc power supply.

Allow the photovoltaic cell normal power supply, make the photovoltaic DC-to-AC converter work of normally being incorporated into the power networks, can obtain from DC side see into the noise source internal impedance be:

$Z_x=\frac{1}{K_z}(\frac{{K_z{R}_{\mathrm{std}}{U}_t|}_{Z_x=R_{\mathrm{std}}}}{{U_t|}_{Z_x=\mathrm{SMPS}}}-\frac{{K_z{U}_t{R}_{\mathrm{std}}|}_{Z_x=R_{\mathrm{std}}}}{{U_t|}_{Z_x=0}})$ （7）

$=\frac{{R_{\mathrm{std}}{U}_t|}_{Z_x=R_{\mathrm{std}}}}{{U_t|}_{Z_x=\mathrm{SMPS}}}-\frac{{U_t{R}_{\mathrm{std}}|}_{Z_x=R_{\mathrm{std}}}}{{U_t|}_{Z_x=0}}$

By changing the frequency of signal generator output signal, just can effectively extract photovoltaic DC-to-AC converter at the noise source internal impedance Z of Conducted EMI frequency range (150KHz-30MHz) _x

In order to describe the problem, the validity that checking the inventive method is extracted photovoltaic combining inverter DC side noise source internal impedance has designed experimental verification platform as shown in Figure 4, comprises photovoltaic cell, photovoltaic DC-to-AC converter, load, R﹠amp; S FSC3 spectrum analyzer (9KHz-3GHz), BCP-513 type current probe (150KHz-1GHz), SG-4162AD LODESTAR company signal generator, 50 Ω normal impedances, (this joint is the radiofrequency signal connector to the signal injection sub-miniature A connector, the output voltage of signal generator is injected in circuit, its center line is signal wire, housing is with reference to ground) etc., its research object is the DC side of inverter, and inverter works in from net state.

At first the injection circuit of signal generator is sealed in the dc power supply side of inverter, radiofrequency signal injection circuit pictorial diagram as shown in Figure 5, comprise two 0.1uF every straight-through high capacitance C _g1, C _g2, 10 Ω bypass resistance R _pAnd signal generator; Secondly, substitute the photovoltaic DC-to-AC converter place in circuit with 50 Ω normal impedances, utilize photovoltaic cell to the experiment power supply.The output signal frequency of conditioning signal generator is f ₀(f ₀=0.15,1,2,3,4 ..., 30MHz), access current probe and frequency spectrograph adopt current probe, according to the HF noise signal voltage U in the test philosophy test circuit in Fig. 3 _t1, just can obtain f ₀Z in situation _t’U _M, that is:

$Z_{t^{\&prime;}}{U}_M=K_z{U}_{t1}{Z}_x{|}_{Z_x=R_{\mathrm{std}}}=50{K_z{\mathrm{<figure-callout\; id="1"\; label="U\; t"\; filenames="HDA00002754628000032.png"\; state="\{\{state\}\}">U</figure-callout>}}_t|}_{Z_x=50}---\left(8\right)$

K wherein _z=(Z _n+ 1jw ₀C _g1+ 1jw ₀C _g2) R _p+ 1, w ₀=2 Π f ₀, Z _nBe signal source internal impedance 50 Ω, C _g1=C _g2=0.1uF, R _p=10 Ω.

With the normal impedance short circuit, give the work of experimental system normal power supply, utilize HF noise signal voltage U in the current probe test circuit according to the test philosophy in Fig. 3 _t2, can obtain f ₀Z in situation _in', that is:

${Z_{\mathrm{in}}}^{\&prime;}=50K_z{U}_{t2}{|}_{Z_x=50}{/U}_{t2}{|}_{Z_x=0}---\left(9\right)$

With photovoltaic combining inverter insert experiment circuit, utilize photovoltaic cell to work on power to inverter.When inverter works, utilize HF noise signal voltage U in the current probe test circuit according to the test philosophy in Fig. 3 _t3, can obtain f ₀Photovoltaic combining inverter DC side noise source internal impedance Z in situation _x, that is:

$Z_x=50U_{t3}{|}_{Z_x=50}/U_{t3}{|}_{Z_x=\mathrm{SMPS}}-50U_{t3}{|}_{Z_x=50}/U_{t3}{|}_{Z_x=0---\left(10\right)}$

According to above-mentioned testing procedure, change one by one the high-frequency signal output frequency f of signal generator ₀Adopt respectively 0.15,1,2,3,4 ..., the 30MHz frequency, measure the detection voltage swing of current probe under every kind of signal frequency, according to formula (8), (9), (10) and testing procedure and test condition, can obtain photovoltaic DC-to-AC converter DC side noise source internal impedance as shown in Figure 6.

Claims (6)

1. the extraction circuit of photovoltaic combining inverter DC side noise source internal impedance, comprise direct voltage source, signal source, current probe, spectrum analyzer and combining inverter, it is characterized in that, the negative pole of combining inverter DC side is connected with signal source by RF cable, and described signal source is connected to the negative pole of direct voltage source; The positive pole of described direct voltage source is connected by the positive pole of wire with the combining inverter DC side, and described wire is provided with the single current probe; Described single current probe is connected to spectrum analyzer.

2. the extraction circuit of photovoltaic combining inverter DC side noise source internal impedance according to claim 1, it is characterized in that, described signal source comprises signal generator, the internal impedance of signal generator output port is 50 Ω, connect respectively capacitance of the two-way of described signal generator output port forms series circuit, and described series circuit is in parallel with a bypass resistance again.

3. the extraction circuit of photovoltaic combining inverter DC side noise source internal impedance according to claim 2, is characterized in that, the capacitance of described capacitance is 0.1uF, and the resistance of bypass resistance is 10 Ω.

4. the extraction circuit of according to claim 1,2 or 3 described photovoltaic combining inverter DC side noise source internal impedances, is characterized in that, described direct voltage source is the photovoltaic cell group.

5. utilize the extracting method of the photovoltaic combining inverter DC side noise source internal impedance of circuit as claimed in claim 1, it is characterized in that, comprise the steps:

(1) direct voltage source and signal source are connected to the DC side of combining inverter;

(2) substitute the combining inverter place in circuit with normal impedance, the output signal frequency f in conditioning signal source ₀, then access current probe and spectrum analyzer, the HF noise signal voltage U in metering circuit _t1

(3) with the normal impedance short circuit, give the work of circuit normal power supply, utilize the HF noise signal voltage U in the current probe metering circuit _t2

(4) with combining inverter alternate standard impedance place in circuit, when inverter works, utilize the HF noise signal voltage U in the current probe metering circuit _t3

(5) magnitude of voltage that obtains according to step (2), (3) and (4), calculating noise source internal impedance is:

Wherein, R _stdBe normal impedance;

(6) change one by one the high-frequency signal output frequency f of signal source ₀, f ₀=0.15,1,2 ..., N ..., 30MHz, wherein N is integer, repeating step (2) is measured magnitude of voltage and noise source internal impedance under each signal frequency to (5).

6. the extracting method of photovoltaic combining inverter DC side noise source internal impedance according to claim 5, is characterized in that, the normal impedance in described step (2) is 50 Ω.

Images