CN103091558B - The extraction circuit of photovoltaic combining inverter direct current side noise source internal impedance and method - Google Patents

Abstract

The invention discloses a kind of extraction circuit and method of photovoltaic combining inverter direct current side noise source internal impedance.Extract circuit and comprise direct voltage source, signal source, current probe, spectrum analyzer and combining inverter, the negative pole of combining inverter DC side is connected with signal source by RF cable, and signal source is connected to the negative pole of direct voltage source; The positive pole of direct voltage source is connected by the positive pole of wire with combining inverter DC side, and wire is provided with single current probe; Single current probe is connected to spectrum analyzer.Utilizing the HF noise signal voltage extracted in circuit measuring circuit, by changing the high-frequency signal output frequency of signal source one by one, just effectively can extract the noise source internal impedance of photovoltaic combining inverter in Conducted EMI frequency range (150KHz-30MHz).The present invention can instruct the conducted EMI noise specificity analysis of photovoltaic combining inverter DC side and the design of electromagnetic interface filter, and the solution for the Conducted EMI problem of photovoltaic combining inverter DC side provides effective theoretical solution.

Description

The extraction circuit of photovoltaic combining inverter direct current side noise source internal impedance and method

Technical field

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

Background technology

Along with the day by day in short supply of traditional energy and the problem of environmental pollution that causes thereof are 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, along with the fast development of Power Electronic Technique, photovoltaic generation and interconnection technology thereof are widely applied, but the power electronic devices that photovoltaic combining inverter adopts in a large number will cause very serious emc issue to electrical network, high dv/dt, di/dt of existing in the DC converting part of wherein combining inverter are one of reasons causing system conductive electromagnetic interference problem.In addition, the chip of high frequency, large scale integrated circuit and the Conducted EMI problem making DC side of selecting of components and parts become increasingly conspicuous, but in order to effectively solve the Conducted EMI problem of DC side, designing efficient Conducted EMI wave filter is one of most effective method, but during design Conducted EMI wave filter, noise source internal resistance must be known, Conducted EMI wave filter so just can be made to reach optimum filtering performance.Therefore the technique study carrying out the extraction of noise source internal impedance for photovoltaic combining inverter DC side is absolutely necessary.

Current electromagnetic compatibility standard is the compulsory standard of produce market access, electrically and electronic product no matter at home or international marketing, all must reach corresponding EMC standard and just can commercially sell.Therefore, the suppression of electromagnetic interference (EMI) (EMI) noise emission is electrically and the major issue must considered in electronic device design and manufacture process, suppress usually to adopt empirical value method design Conducted EMI wave filter to the conducted EMI noise of DC power-supply system at present, because empirical value method does not consider the matching problem between noise source impedance and loaded impedance, thus the Conducted EMI wave filter designed often is difficult to have good filtering performance, the main cause causing this situation to occur be for photovoltaic combining inverter DC side noise source internal impedance extract there is no a kind of system, effective method, thus the assessment of impedance matching property cannot be carried out.

Summary of the invention

Technical matters to be solved by this invention is the defect overcoming prior art existence, proposes a kind of photovoltaic combining inverter direct current side noise source internal impedance extracting method based on single current probe.The method effectively can extract photovoltaic combining inverter direct current side noise source internal impedance, instruct the conducted EMI noise specificity analysis of photovoltaic combining inverter DC side and the design of electromagnetic interface filter, the solution for the Conducted EMI 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 inspection DC power-supply system Electro Magnetic Compatibility.In order to make DC side, there is good Electro Magnetic Compatibility, the conducted EMI noise that it produces must be suppressed, and Conducted EMI wave filter is the Main Means realizing conducted EMI noise suppression, in order to design efficient electromagnetic interface filter, the noise source internal impedance of photovoltaic combining inverter DC side must be known.Double-current probe method extracts one of comparatively effective 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 photovoltaic combining inverter DC side, the concrete technical scheme of the circuit of employing is as follows:

The extraction circuit of photovoltaic combining inverter direct current 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 combining inverter DC side, and described wire is provided with 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 signal generator is equivalent to the radio-frequency voltage source that an internal impedance is 50 Ω, the two ends of this voltage source capacitance of connecting respectively 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) combining inverter place in circuit is substituted by 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) by normal impedance short circuit, to the work of circuit normal power supply, the HF noise signal voltage U in current probe metering circuit is utilized _t2;

(4) by combining inverter alternate standard impedance place in circuit, when inverter normally works, the HF noise signal voltage U in current probe metering circuit is utilized _t3;

(5) according to the magnitude of voltage that step (2), (3) and (4) obtain, 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 _stdfor normal impedance, U _t1for normal impedance substitutes the HF noise signal voltage in the circuit that lower current probe records, U _t2for the HF noise signal voltage in the circuit that current probe under normal impedance short-circuit conditions records, U _t3for the HF noise signal voltage in the circuit that current probe when combining inverter place in circuit works records;

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

For the extraction of photovoltaic combining inverter direct current side noise source internal impedance, the present invention devises and effectively extracts circuit, and propose concrete internal impedance extracting method, for the diagnosis of the DC side conducted EMI noise of photovoltaic combining inverter, analysis and inhibition provide effective theory support, and there is very large practical application value, provide effective reference for improving photovoltaic combining inverter DC side Conducted Electromagnetic compatibility feature.

Accompanying drawing explanation

Fig. 1 is the schematic diagram adopting single current probe method to extract DC power-supply system noise source internal impedance.

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

Fig. 3 is that embodiment of the present invention combining inverter direct current side noise source internal impedance extracts schematic diagram.

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

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

Fig. 6 is that photovoltaic combining inverter direct current side noise source internal impedance extracts result.

Embodiment

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

The noise source internal impedance be illustrated in figure 1 based on the DC power-supply system of single current probe extracts schematic diagram, comprising signal source, current probe, frequency spectrograph and impedance to be measured, wherein signal source is High frequency injection signals, current probe is that high-frequency signal detects and uses, and cable equiva lent impedance is the resistance of cable self, appearance, sense characterisitic parameter.Because signal generator provides radiofrequency signal in experimental system, its power is less, withstand voltage also lower, the high pressure being subject to tested DC power-supply system in order to avoid it damages, need at its signal output part series connection capacitance, according to electromagnetic compatibility standard regulation, the conventionally test frequency range of conducted electromagnetic interference noise is 150KHz-30MHz, as long as therefore capacitance capacitance size is chosen suitable, just can ensure that the output signal of signal generator is effectively transmitted.Simultaneously in order to ensure that the signal that system under test (SUT) direct current supply is effectively powered and signal generator exports effectively enters system under test (SUT), for impedance extraction, need on primary circuit basis a bypass resistance in parallel, resistance sizes is tested according to impedance extraction to be needed to determine.

Be illustrated in figure 2 the equivalent circuit diagram of Fig. 1 impedance extraction principle, wherein U _mfor the output voltage of signal source, Z _nfor the internal impedance of signal source, C _g1and C _g2for 0.1uF capacitance, R _pbe 10 Ω bypass resistances, Z _tfor current probe mutual inductive impedance on the line, Z _cfor cable impedance.

Signal source U _mcircuit I is produced in the line during normal work _w, according to the equivalent electrical circuit of Fig. 2, four equations of this circuit can be obtained:

$\left\{\begin{array}{c}{u}_{aa\′}=I_w(Z_t+Z_c+Z_x)\\ I_p=u_{a{a}^{\′}}/R_p\\ I_M=I_w-I_p\\ U_M=I_M(Z_n+1/\mathrm{jw}{C}_{g1}+1/\mathrm{jw}{C}_{g2})+u_{aa\′}\end{array}\right.---\left(1\right)$

Wherein I _pfor flowing through the electric current of bypass resistance branch road, I _mfor signal source branch road total current, can obtain 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:

$U_M=I_w\left\{\begin{array}{c}(Z_n+1/\mathrm{jw}{C}_{g1}+1/\mathrm{jw}{C}_{g2}+Z_t+Z_c-\frac{(Z_t+Z_c)(Z_n+1/\mathrm{jw}{C}_{g1}+1/\mathrm{jw}{C}_{g2})}{R_p})\\ -(\frac{(Z_n+1/\mathrm{jw}{C}_{g1}+1/\mathrm{jw}{C}_{g2})}{R_p}+1)Z_x\end{array}\right\}---\left(3\right)$

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

Wherein:

${Z_{\mathrm{in}}}^{\′}=Z_n+1/\mathrm{jw}{C}_{g1}+1/\mathrm{jw}{C}_{g2}+Z_t+Z_c-\frac{(z_t+Z_c)(Z_n+1/\mathrm{jw}{C}_{g1}+1/\mathrm{jw}{C}_{g2})}{R_p}$

$k_z=\frac{(Z_n+1/\mathrm{jw}{C}_{g1}+1/\mathrm{jw}{C}_{g2})}{R_p}+1$

Once Z _n, C _g1, C _g2and R _pdetermine, then K _zfor the fixed value that can calculate.Therefore, the expression formula that can obtain tested impedance is:

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

Can be calculated wherein Z _{t '}for fixed value, and only relevant with the inherent parameters detecting current probe.Holding signal source exports constant, then for given frequency, and Z _{t '}u _mit is a fixed value.By a unknown impedance known measuring resistance R _stdsubstitute, and K _zr _std>>Z _in', then

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

By Z _xshort circuit then can survey impedance Z _in',

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

When measure photovoltaic combining inverter direct current side noise source internal impedance time, its test philosophy figure as shown in Figure 3, wherein V _dfor DC power supply.

Allow photovoltaic cell normal power supply, make the normal grid-connected work of photovoltaic DC-to-AC converter, then the noise source internal impedance that can obtain entering viewed from DC side is:

$Z_x=\frac{1}{K_z}(\frac{{K_z{R}_{\mathrm{std}}{U}_t|}_{Z_x=R_{\mathrm{std}}}}{{U_t|}_{Z_x=\mathrm{SMPS}}}-\frac{{K_z{U}_t{R}_{\mathrm{std}}|}_{Z_x=R_{\mathrm{std}}}}{{U_t|}_{Z_x=0}})$ （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, the noise source internal impedance Z of photovoltaic DC-to-AC converter in Conducted EMI frequency range (150KHz-30MHz) just effectively can be extracted _x.

In order to describe the problem, the validity that checking the inventive method is extracted photovoltaic combining inverter direct current side noise source internal impedance, devise experimental verification platform as shown in Figure 4, comprise photovoltaic cell, photovoltaic DC-to-AC converter, load, R & 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 radiofrequency signal connector to 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.

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 photovoltaic DC-to-AC converter place in circuit by 50 Ω normal impedances, utilize photovoltaic cell to 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, adopts current probe, according to the HF noise signal voltage U in the test philosophy test circuit in Fig. 3 _t1, then just f can be obtained ₀z in situation _{t '}u _m, that is:

$Z_{t^{\′}}{U}_M=K_z{U}_{t1}{Z}_x{|}_{Z_x=R_{\mathrm{std}}}=50{K_z{U}_{t1}|}_{Z_x=50}---\left(8\right)$

Wherein K _z=(Z _n+ 1jw ₀c _g1+ 1jw ₀c _g2) R _p+ 1, w ₀=2 Π f ₀, Z _nfor singal source resistance anti-50 Ω, C _g1=C _g2=0.1uF, R _p=10 Ω.

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

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

By photovoltaic combining inverter insert experiment circuit, photovoltaic cell is utilized to work on power to inverter.When inverter normally works, utilize the HF noise signal voltage U in current probe test circuit according to the test philosophy in Fig. 3 _t3, then f can be obtained ₀photovoltaic combining inverter direct current 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 the high-frequency signal output frequency f of signal generator one by one ₀adopt 0.15 respectively, 1,2,3,4 ..., 30MHz frequency, the detection voltage swing of current probe is measured under often kind of signal frequency, according to formula (8), (9), (10) and testing procedure thereof and test condition, photovoltaic DC-to-AC converter direct current side noise source internal impedance can be obtained as shown in Figure 6.

Claims (5)

1. the extraction circuit of photovoltaic combining inverter direct current 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 combining inverter DC side, and described wire is provided with single current probe; Described single current probe is connected to spectrum analyzer; Described signal source comprises signal generator, and the internal impedance of signal generator output port is 50 Ω, and the two-way of described signal generator output port is connected capacitance C respectively _g1, C _g2form series circuit, capacitance C _g1one end connection signal generator, the other end connects the negative pole of direct voltage source; Capacitance C _g2one end connection signal generator, the other end connects the negative pole of combining inverter DC side, and described series circuit is in parallel with a bypass resistance again, and one end of bypass resistance connects the negative pole of direct voltage source, and the other end connects the negative pole of combining inverter DC side.

2. the extraction circuit of photovoltaic combining inverter direct current side noise source internal impedance according to claim 1, is characterized in that, the capacitance of described capacitance is 0.1uF, and the resistance of bypass resistance is 10 Ω.

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

4. utilize the extracting method of the photovoltaic combining inverter direct current 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) combining inverter place in circuit is substituted by 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) by normal impedance short circuit, to the work of circuit normal power supply, the HF noise signal voltage U in current probe metering circuit is utilized _t2;

(4) by combining inverter alternate standard impedance place in circuit, when inverter normally works, the HF noise signal voltage U in current probe metering circuit is utilized _t3;

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

$Z_x=\frac{R_{\mathrm{std}}{U}_{t1}{|}_{Z_x=R_{\mathrm{std}}}}{U_{t3}{|}_{Z_x=\mathrm{SMPS}}}-\frac{U_{t1}{R}_{\mathrm{std}}{|}_{Z_x=R_{\mathrm{std}}}}{U_{t2}{|}_{Z_x=0}}$

Wherein, R _stdfor normal impedance, Z _x=SMPS represents the internal impedance of combining inverter during combining inverter place in circuit, the i.e. internal impedance of tested noise source;

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

5. the extracting method of photovoltaic combining inverter direct current side noise source internal impedance according to claim 4, is characterized in that, the normal impedance in described step (2) is 50 Ω.