CN103439615B - The equivalent conversion method of output voltage waveform distortion degree of photovoltaic inverter - Google Patents
The equivalent conversion method of output voltage waveform distortion degree of photovoltaic inverter Download PDFInfo
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- CN103439615B CN103439615B CN201310395342.3A CN201310395342A CN103439615B CN 103439615 B CN103439615 B CN 103439615B CN 201310395342 A CN201310395342 A CN 201310395342A CN 103439615 B CN103439615 B CN 103439615B
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Abstract
The present invention relates to a kind of equivalent conversion method of output voltage waveform distortion degree of photovoltaic inverter, comprise and obtain photovoltaic DC-to-AC converter to be measured; Connect equivalent testing capacitor unit; Connection signal capture card; Connect computing machine and carry out signals collecting, obtain photovoltaic DC-to-AC converter actual output voltage waveform; Estimation photovoltaic DC-to-AC converter actual output voltage waveform distortion equivalent coefficient; Change photovoltaic DC-to-AC converter to be measured; Select the steps such as suitable test resistance.Fundamental voltage value <i>U in the estimation process of degree of distortion equivalent coefficient
1</i> launches to obtain by the Fast Fourier Transform (FFT) of signal, equivalent tank magnitude of voltage <i>U</iGreatT.Gr eaT.GT is obtained by testing capacitor, and equivalent tank coefficient η is different according to the difference of output waveform.Equivalent conversion method of the present invention, the estimated value computation process of testing its voltage wave shape distortion degree is simple, convenient, is convenient to the inverter model that photovoltaic system deviser selects to be suitable for fast, and is preliminary test inverter performance supplying method foundation.
Description
Technical field
The invention belongs to output voltage waveform distortion degree of photovoltaic inverter technical field of analysis and detection, particularly relate to a kind of equivalent conversion method of output voltage waveform distortion degree of photovoltaic inverter.
Background technology
Inverter, also known as feed regulator isolator, can be divided into self power supply to use and grid-connected use two kinds according to the purposes of inverter in photovoltaic generating system.Square-wave inverter, ladder inverter, sinewave inverter and Three-Phase Inverter can be divided into again according to waveform modulated mode.Functional structure is generally made up of boosting loop and inversion bridge type return.Boosting loop exports the DC voltage needed for controlling the dc voltage boost of solar cell to inverter; Inversion bridge type return then equivalently converts the DC voltage after boosting to the alternating voltage of conventional frequency.Inverter is formed primarily of on-off elements such as transistors, by allowing on-off element repeat on-off regularly, direct current input being become and exchanges output.Certainly, so merely by open and close loop produce inverter output waveforms and impracticable.Generally need to adopt high-frequency pulsed width modulation (SPWM), make the voltage width stenosis near sinusoidal wave two ends, the voltage width of sinusoidal wave central authorities broadens, and within the semiperiod, allow on-off element all the time by certain frequency towards a direction action, form a pulse wave train (intending sinusoidal wave) like this.Then pulsating wave is allowed to form sine wave by simple wave filter.
Wherein, the key technical indexes of photovoltaic DC-to-AC converter has the degree of stability of output voltage, the waveform distortion of specified output frequency and output voltage.Higher harmonic current due to inverter output can produce the added losses of eddy current on inductive load, if inverter waveform distortion is excessive, parts can be caused to generate heat serious, unfavorable payload security, hinders system works efficiency.
Conventional degree of distortion detecting instrument measuring principle is broadly divided into two large classes: first-harmonic scalping method and Spectral Analysis Method.Generally analog measuring instrument adopts first-harmonic scalping method, but its shortcoming needs to provide undistorted fundamental signal, and its low frequency measurement precision is low.Spectral Analysis Method measures the method for each harmonic with frequency analyzer to calculate waveform distortion, but the instrument price adopting this kind of method costly.Precisely not yet grasp automatically by tracking technique China present stage for frequency.
Summary of the invention
The object of the invention is to overcome above-mentioned defect of the prior art, provide a kind of simply, the equivalent conversion method of output voltage waveform distortion degree of photovoltaic inverter fast.
Principle of the present invention:
The present invention utilizes the effective voltage of output voltage waveforms and frequency and capacitor real work and the relation of watt current and temperature rise, obtains output voltage waveform by the duty measuring capacitor.Under active computer technology, contrast the existing measured signal quantized by grouping, recombination data capture card, the data of component are being carried out to process calculating, based on FFT principle (Fast Fourier Transform (FFT)), calculated the Equivalent calculation method of the output voltage waveforms distortion angle value of photovoltaic DC-to-AC converter by degree of distortion computing formula.
Technical scheme taked for achieving the above object is:
An equivalent conversion method for output voltage waveform distortion degree of photovoltaic inverter, is characterized in that, said method comprising the steps of:
(1) photovoltaic DC-to-AC converter to be measured is obtained;
(2) equivalent testing capacitor unit is connected;
(3) connection signal capture card;
(4) connect computing machine and carry out signals collecting, obtain photovoltaic DC-to-AC converter actual output voltage waveform;
(5) photovoltaic DC-to-AC converter actual output voltage waveform distortion equivalent coefficient is estimated;
(6) photovoltaic DC-to-AC converter to be measured is changed;
(7) suitable test resistance is selected;
(8) step (3) is continued;
In described step (5), the estimation equation of output voltage waveform distortion degree of photovoltaic inverter equivalent coefficient is according to degree of distortion computing formula
derive, the difference because of output waveform has two kinds of estimation equations:
1) output waveform is effective resonance potential V of sinusoidal wave testing capacitor
rmsci=V
pP/ 1.04, effective resonance current I
rmsci=I
pp/ 2.08, peak power loss p
rmsci=V
2 rmsci× 2 π f × C × tg δ
max(f), d
v/ d
t=V
pP/ τ, according to output voltage waveforms degree of distortion formula
derive degree of distortion equivalent coefficient
wherein, fundamental voltage value is launched to obtain by the Fast Fourier Transform (FFT) of signal;
2) output waveform is square wave, effective resonance potential V of testing capacitor
rmsci=V
pp/ 1.04/2
0.5, effective resonance current I
rmsci=I
pP/ 2.08/2
0.5, peak power loss p
rmsci=V
2 rmsci× 2 π f × C × tg δ
max(f), d
v/ d
t=V
pP/ τ, according to output voltage waveforms degree of distortion formula
derive degree of distortion equivalent coefficient
wherein, fundamental voltage value is launched to obtain by the Fast Fourier Transform (FFT) of signal.
Described equivalent signal collection point have X ,+, O, △ 4 points.
Described " equivalence " is product total power signal being scaled testing capacitor resonance potential value and coefficient.
Described equivalent conversion method is used for the minimum input voltage 12V of photovoltaic DC-to-AC converter, within the scope of maximum output voltage 360V.
The value that described equivalent conversion method obtains is estimated value, not true value.
The present invention is in conjunction with photovoltaic DC-to-AC converter work, the key control point of the output voltage waveforms degree of distortion of handling characteristics and photovoltaic DC-to-AC converter, performance model analog computation method carries out usefulness estimation, fundamental voltage value in analog computation is obtained by Fast Fourier Transform (FFT), total power signal is scaled the product of testing capacitor resonance potential value and coefficient, for the transport property of this main Researching The Equivalent internal components electronics of resonance coefficient, free carrier cloth inning can be calculated by Poisson equation, the cloth inning of trapped electron, use again and solve coupled nonlinear equations to estimate parameter value.The present invention not only solves output voltage waveform distortion degree of photovoltaic inverter estimation problem, also sum up the relation of effective voltage and watt current and the temperature rise utilizing output voltage waveforms and frequency and capacitor real work, obtain output voltage waveform by the duty measuring capacitor.
The equivalent conversion method of output voltage waveform distortion degree of photovoltaic inverter of the present invention, test its voltage wave shape distortion degree and eliminate loaded down with trivial details a large amount of computation processes, the substitute is simple, equivalent estimated value method, thus the inverter model allowing photovoltaic system deviser select to be suitable for more quickly and easily, for preliminary test inverter aspect of performance, also provide method foundation.
Accompanying drawing explanation
Fig. 1 is the equivalent conversion method process flow diagram of output voltage waveform distortion degree of photovoltaic inverter of the present invention;
Fig. 2 is that the equivalent signal of the equivalent conversion method of output voltage waveform distortion degree of photovoltaic inverter of the present invention gathers point diagram.
Embodiment
As Fig. 1, the equivalent conversion method of output voltage waveform distortion degree of photovoltaic inverter of the present invention, detailed process is: (1) obtains photovoltaic DC-to-AC converter unit to be measured, obtains rated voltage and load current value; (2) connect equivalent testing capacitor unit, its effect draws output voltage waveform by the relation of equivalent capacity effective voltage and watt current and temperature rise; (3) connection signal capture card unit, its effect does hardware preparation for gathering voltage output signal; (4) computer unit is connected, carry out signals collecting, collection point with reference to Fig. 2 equivalent signal collection point X ,+, O, △ 4 points gather, obtain photovoltaic DC-to-AC converter actual output voltage waveform, obtain fundamental voltage value by Fast Fourier Transform (FFT), obtain equivalent tank magnitude of voltage by testing capacitor; (5) by distortion estimation formula estimation degree of distortion.Distortion estimation formula is:
Difference because of output waveform has two kinds of estimation equations:
1) output waveform is effective resonance potential V of sinusoidal wave testing capacitor
rmsci=V
pP/ 1.04, effective resonance current I
rmsci=I
pp/ 2.08, peak power loss p
rmsci=V
2 rmsci× 2 π f × C × tg δ
max(f), d
v/ d
t=V
pP/ τ, according to output voltage waveforms degree of distortion formula
derive degree of distortion equivalent coefficient
wherein, fundamental voltage value is launched to obtain by the Fast Fourier Transform (FFT) of signal;
2) output waveform is square wave, effective resonance potential V of testing capacitor
rmsci=V
pp/ 1.04/2
0.5, effective resonance current I
rmsci=I
pP/ 2.08/2
0.5, peak power loss p
rmsci=V
2 rmsci× 2 π f × C × tg δ
max(f), d
v/ d
t=V
pP/ τ, according to output voltage waveforms degree of distortion formula
derive degree of distortion equivalent coefficient
wherein, fundamental voltage value is launched to obtain by the Fast Fourier Transform (FFT) of signal.
The value that described equivalent conversion method obtains is estimated value, not true value.
(6) photovoltaic DC-to-AC converter to be measured is changed; (7) suitable test resistance is selected; (8) step (3) is continued.
This equivalent conversion method is used for the minimum input voltage 12V of photovoltaic DC-to-AC converter, within the scope of maximum output voltage 360V; The value obtained is estimated value, not true value.Described equivalent conversion method of the present invention is used for the minimum input voltage 12V of photovoltaic DC-to-AC converter, within the scope of maximum output voltage 360V.
Embodiment 1
Obtain photovoltaic DC-to-AC converter rated output capacity 3kVA to be measured, specified battery tension 48VDC, no-load current 0.42A, connect equivalent testing capacitor unit, data acquisition card unit and computer unit, with reference to Fig. 2 equivalent signal collection point X, +, O, △ 4 points carry out signals collecting, it is sinusoidal wave for obtaining photovoltaic DC-to-AC converter actual output voltage waveform, 220V transforms output, output frequency 50HZ, frequency error 0.05%, inversion efficiency 90%, calculate by method step and obtain equivalent capacity test voltage value 221.3V, Fourier transform fundamental voltage value 220.9V, obtain distortion rate according to waveform distortion factor equivalent formulation and be approximately 3.4%, rounding waveform distortion factor value is 4%.Correspondingly with producer given parameters value look into, distortion rate estimation is correct.
Embodiment 2
Obtain photovoltaic DC-to-AC converter rated output capacity 3kVA to be measured, specified battery tension 48VDC, no-load current 0.42A, connect equivalent testing capacitor unit, data acquisition card unit and computing machine list, with reference to Fig. 2 equivalent signal collection point X, +, O, △ 4 points carry out signals collecting, it is sinusoidal wave for obtaining photovoltaic DC-to-AC converter actual output voltage waveform, 110V transforms output, output frequency 60HZ, frequency error 0.05%, inversion efficiency 90%, calculate by method step and obtain equivalent capacity test voltage value 110.3V, Fourier transform fundamental voltage value 110.9V, obtain distortion rate according to waveform distortion factor equivalent formulation and be approximately 3.3%, rounding waveform distortion factor value is 4%.Correspondingly with producer given parameters value look into, distortion rate estimation is correct.
Embodiment 3
Obtain photovoltaic DC-to-AC converter rated output capacity 3kVA to be measured, specified battery tension 48VDC, no-load current 0.42A, connect equivalent testing capacitor unit, data acquisition card unit and computing machine list, with reference to Fig. 2 equivalent signal collection point X, +, O, △ 4 points carry out signals collecting, obtaining photovoltaic DC-to-AC converter actual output voltage waveform is square wave, 220V transforms output, output frequency 50HZ, frequency error 0.05%, inversion efficiency 90%, calculate by method step and obtain equivalent capacity test voltage value 220.2V, Fourier transform fundamental voltage value 221.3V, obtain distortion rate according to waveform distortion factor equivalent formulation and be approximately 4.0%, with producer given parameters value corresponding to look into, distortion rate estimation is correct.
Claims (1)
1. an equivalent conversion method for output voltage waveform distortion degree of photovoltaic inverter, is characterized in that, said method comprising the steps of:
(1) photovoltaic DC-to-AC converter to be measured is obtained;
(2) equivalent testing capacitor unit is connected;
(3) connection signal capture card;
(4) connect computing machine and carry out signals collecting, obtain photovoltaic DC-to-AC converter actual output voltage waveform, obtain fundamental voltage value by Fast Fourier Transform (FFT), obtain equivalent tank magnitude of voltage by testing capacitor;
(5) degree of distortion equivalent coefficient estimation equation is utilized to estimate photovoltaic DC-to-AC converter actual output voltage waveform distortion equivalent coefficient;
(6) photovoltaic DC-to-AC converter to be measured is changed;
(7) suitable test resistance is selected;
(8) step (3) is continued;
In above-mentioned steps (5), degree of distortion equivalent coefficient estimation equation is derived by degree of distortion computing formula, and described degree of distortion computing formula is
When output waveform is sinusoidal wave, degree of distortion equivalent coefficient estimation equation is:
When output waveform is square wave, degree of distortion equivalent coefficient estimation equation is:
Wherein, fundamental voltage value is launched to obtain by the Fast Fourier Transform (FFT) of signal.
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