Abstract: Has analyzed each kind of load (including pure resistive load, perceptual load, accommodates load, misalignment load), high efficiency frequency conversion power source’s input level. The experimental result indicated that this frequency conversion power source the output voltage and the frequency is very stable under each heterogeneity’s load.
Key word: Frequency changer; Input level; Waveform analysis
Introduction
It is well known, we use the power frequency is 50Hz, but, in the practical life, sometimes needs the supply frequency is not 50Hz, this needs the frequency conversion power source. To a power source, the user expected that it under each nature’s load, can output the stable voltage, the frequency conversion power source is not exceptional. Therefore, it is necessary to study the frequency conversion power source in each nature load (pure resistance, perception, accommodates nature, misalignment) under input level.
1 testing plan
This experiment’s wiring diagram as shown in Figure 1.
50Hz three-phase network voltage after frequency changer rectification inversion, the output frequency invariable (user may adjust output frequency voluntarily) sine wave, after the LC filter, then passes through the boosting transformer (function is pressure-rise and isolation) adds to the three-phase load. The three-phase load may be the pure resistance, the perception, Rong Xinghe the misalignment.
This experiment expectation obtains the result is, when frequency changer’s output voltage and output frequency hypothesis for fixture, this frequency conversion electrical power unit can under each nature load, output the stable voltage and the frequency.
2 parameter choices
2.1 frequency changers
This experimental frequency changer is SIEMENS Corporation’s MIDIMASTERVECTOR (MDV), its output is 7.5kW, fixed input voltage 380V, output voltage adjustable, input frequency 50Hz, output frequency adjustable.
2.2 transformers and filter parameters
Because the frequency changer input rated voltage is 380V, output voltage in the 0~380V scope adjustable, this experiment establishes the frequency changer output voltage most to be high is 300V, therefore, needs a boosting transformer, changes the ratio is 300/380, makes to add in the load both sides voltage is 380V.
Because uses the filter circuit is the LC filter, its filter inductance and the electric capacity must satisfy-like (1)
1/2 Mu (root number LC) <= root number f1fs (1)
In the formula: fs is frequency changer’s turn-on frequency, fs=4kHz;
f1 takes is fs.
Therefore root number f1fs= root number (800×4000) =1789Hz
If takes L=7mH, C=1.5μF, then =1/[2π (root number LC)]
1553Hz satisfies-like (1).
2.3 load parameters
In the pure resistive load experiment, each uses 5 250Ω, rated power 200W resistance series; In the perceptual load experiment, each uses 3 250Ω/200W resistances to be parallel, then again with 62mH inductance series composition perceptual load; In accommodates in the load experiment, each uses 3 10Ω/250W resistance series, again with 70μF the electric capacity series composition accommodates the load, moreover, each uses 5 250Ω/200W resistances to be parallel, again with 70μF the electric capacity parallel also composes accommodates the load; In the misalignment load experiment, uses the rated voltage is 800V, the nominal current is the 20A rectification bridge takes the misalignment load.
3 experiment processes and analysis
According to Figure 1 wiring, three-phase filter inductance L is 7mH, the three-phase filter electric capacity is 1.5μF, the transformer uses △/Y the connection, changes compared to is 300/380, the frequency changer output frequency hypothesis is 60Hz, then meets the heterogeneity the load to carry on the experiment.
3.1 pure resistive load experiments and analysis
The three-phase load uses five 250Ω/200W ceramic resistor series, the output voltage is 300V, when confirmed when all wiring do not have the question, starts to test, obtains profile as shown in Figure 2. The analysis and showing are as follows:
1), because the frequency changer output voltage is 300V, then transformer input voltage close 300V, but the transformer changes the ratio is 300/380, therefore, the transformer output voltage is 380V theoretically, its peak value is 537V;
2) tests, through the observation chart 2 the profile, obtains the transformer output voltage peak value actual value is 540V, close theoretical value;
3) with the spectrum analyzer observation overtone distribution, saw 4kHz the overtone and the 60Hz fundamental wave difference is biggest, has 30dB, namely the overtone approximately composes the fundamental wave 3.16%.
3.2 perceptual load experiments and analysis
The load changes into the perception Figure 1, each uses 3 250Ω/200W resistances to be parallel, with the 63mH inductance series, the three-phase load meets the star type, the output voltage is 300V again, when confirmed after all wiring do not have the question, starts to test, obtains profile as shown in Figure 3. The analysis and showing are as follows:
1) with the spectrum analyzer observation overtone distribution, discovered that in this kind of situation in 300Hz the overtone and the 4kHz,8kHz overtone and the 60Hz fundamental wave differs about 30dB, namely the harmonic components approximately compose the fundamental wave 3.16%, other number of times’s harmonic content is lower, indicated that the filter effect is good;
2) to further improve the profile, attempts trades each filter inductance by 7mH is 10mH, observes the overtone distribution again, discovered that the higher harmonic (4kHz,8kHz) differs 33.6dB with the fundamental wave, the profile has the improvement, as shown in Figure 4;
3), because this experiment uses the inductance the enamel-insulated wire to be quite thin, cannot withstand the very big electric current, therefore, the frequency changer output voltage adjustment is 230V, this time theoretically the transformer output voltage peak value should be 412V, observation chart 3 the profile, the discovery actual value is 420V, basic close theoretical value.
3.3 accommodate the load experiment and the analysis
3.3.1 resistances and electric capacity series
Load changes into three compatible load Figure 1, each by 3 10Ω/250W resistance series, again with 70μF the electric capacity series, the frequency changer output voltage is 298.4V, obtains profile as shown in Figure 5. The analysis and showing are as follows:
With the spectrum analyzer observation overtone distribution condition, discovered that the most higher harmonic for the higher harmonic (4kHz,8kHz), its frequency multiplication and the fundamental wave differs 35dB, namely the harmonic components occupy the fundamental wave 1.8%, the filter effect is good, has the higher harmonic, is because frequency changer’s turn-on frequency is 4kHz.
3.3.2 resistances and the electric capacity are parallel
Changes into again the load each is parallel by 5 250Ω/200W resistances, again with 70μF the electric capacity is parallel, the frequency changer output voltage is 303V, obtains profile as shown in Figure 6.
3.4 misalignment load experiments and analysis
Load changes into the rated voltage Figure 1 is 800V, the nominal current is the 20A rectification bridge takes the misalignment load, the frequency changer output voltage is 300V, after inspecting all wiring do not have the question, starts to test, the experiment situation is as follows:
1) the rectification bridge output voltage profile, as shown in Figure 7, its theoretical value is 515V, the observation profile, the actual value is 520V, differs not in a big way, the experiment effect is alright;
2) the transformer output voltage profile, as shown in Figure 8. With the spectrum analyzer observation overtone distribution, discovered that the overtone is quite fierce, the 300Hz overtone is fiercest, differs 20.6dB with the 60Hz fundamental wave; the 120Hz,240Hz,1.2kHz,4kHz,8kHz overtone is also fierce, the 4kHz overtone and the fundamental wave differ the 28.8dB,8kHz overtone and the fundamental wave differ 34dB;
3) attempts the filter electric capacity by 1.5μF becomes 3μF, discovered that the high-frequency unit overtone has reduces, profile closer sine wave;
4) becomes again the filter inductance by 7mH 10mH, discovered that the overtone distribution changes not obviously.
3.5 experimental result summary
After generalized analysis above experiment profile and data, summarizes as follows:
1), when the frequency changer output frequency hypothesis is 60Hz, the frequency conversion power source outputs the frequency under each nature’s load is also 60Hz, the fluctuation is very small, meets the design requirements;
2) in the pure resistive load situation, the frequency changer output voltage hypothesis is 300V, the frequency conversion power source output voltage peak value is 540V, in 510V~564V scope (theoretical value fluctuation in ±5% scopes);
3) in perceptual load situation, because uses the inductance the enamel-insulated wire to be quite thin, the withstanding electric current is quite small, most 3A, therefore, the frequency changer output voltage adjustment is 230V, this time the frequency conversion power source output voltage peak value is 420V, according to this deduces, if the frequency changer output voltage is 300V, then the frequency conversion power source output voltage peak value is 549V, also in the 510V~564V scope, satisfies the request;
4) in accommodates in the load situation, when resistance and electric capacity series, the frequency changer output voltage is 298.4V, the frequency conversion power source output voltage peak value is 530V; When the resistance and the electric capacity are parallel, the frequency changer output voltage is 303V, the frequency conversion power source output voltage peak value is 540V;
5) in the misalignment load situation, the frequency changer output voltage still the hypothesis was 300V, this time the frequency conversion power source output voltage peak value is 530V, also in the 510V~564V scope, satisfies the request similarly.
4 conclusions
This experiment’s goal is wants to make a high efficiency frequency conversion power source, it should be able under each nature load, to output the stable voltage and the frequency, the voltage hunting in ±5%, namely, if the hypothesis frequency changer output line voltage is 300V, the transformer output line voltage peak value should change in the 510V~564V scope. As a result of the test installation and primary device’s limitation, this experiment has not achieved the ideal effect completely, under each kind of load’s power has not achieved the expectation 7500W (each 2500W). But, in the full use had under equipment’s premise, obtained the quite satisfactory result, besides accommodates the load, under other load’s output voltage is quite stable, basically changes in the 510V~564V scope, and besides the misalignment load (misalignment load because of its own output current not continual characteristic, had decided its overtone distribution is quite surely fierce, is unable with the LC filter to achieve ideal effect well), the filter effect is good, basic control in 3%~5%.
