CN104578807A - Three-phase output voltage balance adjusting method based on phrase voltage control - Google Patents

Abstract

The invention discloses a three-phrase output voltage balance adjusting method based on phrase voltage control. The method comprises the following steps that firstly, sampling on a dc-bus voltage VPN of each phrase of a high-voltage inverter is conducted, secondly, theoretical set values of the phrase voltages are worked out, and finally, the values of amplitude of the adjusted phrase voltages can be worked out. The three-phrase output voltage balance adjusting method based on the phrase voltage control can further overlays three times of harmonic waves on a sine wave modulating signal of the adjusted phrase voltages. Under the condition of sudden changes of a environment, the three-phrase output voltage balance adjusting method based on the phrase voltage control can still keep output voltage balanced, the maximum degree of unbalance of the output voltage is 2%, neutral point excursion is avoided, and damages to a switching element and a motor are reduced. By means of the three-phrase output voltage balance adjusting method based on the phrase voltage control, the utilization ratio of dc-bus voltage is increased by 15%.

Description

Based on the three-phase output voltage balance adjusting method that phase voltage controls

Technical field

The present invention relates to the output adjusting method of high voltage converter, be specifically related to a kind of three-phase output voltage balance adjusting method controlled based on phase voltage.

Background technology

High voltage converter in use, if input or load changing time, the unbalanced situation of busbar voltage can be caused.The H bridge construction of high voltage converter many employings plural serial stage improves capacity, and for Series power module, busbar voltage is unbalanced certainly will cause damage to switching device.In prior art, neutral point excursion technology can be adopted still to maintain balance to the three-phase line voltage ensureing high voltage converter and output to motor, but keep output line voltage balancing technique based under line voltage modulated mode during the asymmetric bypass that is unit of neutral point excursion technology, now phase voltage cannot superpose triple-frequency harmonics, cannot be further improved frequency converter character, so also seldom have investigation and application based on the phase voltage modulation technique of superposition triple-frequency harmonics.

Summary of the invention

In order to solve the problem, the invention discloses a kind of three-phase output voltage balance adjusting method controlled based on phase voltage.

Technical scheme of the present invention is as follows:

Based on the three-phase output voltage balance adjusting method that phase voltage controls, comprise the following steps:

A, every phase DC bus-bar voltage V to high voltage converter _pNsample;

The theory setting value of b, calculating phase voltage:

$V_{\mathrm{PN}\left(\mathrm{mean}\right)}=\frac{1}{n}{\mathrm{\Σ}}_{i=1}^n{V}_{\mathrm{PN}\left(i\right)}---\left(1\right)$

In formula (1), n is power cell number;

Phase voltage amplitude after c, adjustment:

$U_m=V_1^{*}\×\frac{U_{{\mathrm{dc}-\mathrm{rated}}^{*}}}{U_{\mathrm{dc}}}---\left(2\right)$

In formula (2), for the V/f curve of frequency converter, be numerically equal to V _{pN (mean)}; U _dcbe numerically equal to V _pN;

Its further technical scheme is: the sinewave modulation signal of the phase voltage in described step c after adjustment superposes triple-frequency harmonics.

Advantageous Effects of the present invention is:

In the middle of the use procedure of high voltage converter, when input or load changing, method of the present invention can be used, by each power model bus voltage value of real-time sampling, with mean value as benchmark, revise modulating wave voltage magnitude.The present invention can when environmental catastrophe, and still make output voltage keep balance, output voltage degree of unbalance is up to 2%, avoids neutral point excursion, reduces the damage to switching device, and the damage to motor.The present invention has also superposed triple-frequency harmonics in the sinewave modulation signal of phase voltage further, makes DC bus-bar voltage utilance improve 15%.

Accompanying drawing explanation

Fig. 1 is the V/F curve that frequency converter runs.

Fig. 2 is the amplitude change oscillogram of modulation signal.

Fig. 3 is the modulation signal waveform of superposition triple-frequency harmonics.

Embodiment

The three-phase output voltage balance adjusting method controlled based on phase voltage disclosed by the invention, comprises the following steps:

A, every phase DC bus-bar voltage V to high voltage converter _pNsample;

B, the summation of every phase voltage to be averaging as theory setting value again

$V_{\mathrm{PN}\left(\mathrm{mean}\right)}=\frac{1}{n}{\mathrm{\Σ}}_{i=1}^n{V}_{\mathrm{PN}\left(i\right)}---\left(1\right)$

In formula (1), n is power cell number in high voltage converter;

Phase voltage amplitude after c, adjustment:

$U_m=V_1^{*}\×\frac{U_{{\mathrm{dc}-\mathrm{rated}}^{*}}}{U_{\mathrm{dc}}}---\left(2\right)$

In formula (2), be the V/f curve of frequency converter, Fig. 1 is the operation V/f curve that frequency converter is arranged. be numerically equal to V _{pN (mean)}.U _dcfor the busbar voltage sampled value of reality, be numerically equal to V _pN.

Can find out from formula (2), work as U _dcduring reduction, U _mincrease; Work as U _dcduring increase, U _mreduce.Then when load variations or input change, the amplitude of voltage modulated ripple can be corrected, and output voltage is balanced.This invention can when environmental catastrophe, and still make output voltage keep balance, output voltage degree of unbalance is up to 2%, effectively can avoid neutral point excursion, reduces load variations or the damage of input change to motor.When Fig. 2 is DC bus-bar voltage change, the amplitude change oscillogram of modulation signal.In Fig. 2, t ₁~ t ₂time period represents that the output of high voltage converter diminishes suddenly, causes busbar voltage U _dcalso diminish suddenly, now by the method for the invention, have modified the amplitude of modulating wave, make it to adjust from U _mbecome U ₁, increase the amplitude of modulating wave thus make output voltage stabilization; t ₃~ t ₄time period represents that exporting change suddenly greatly, causes busbar voltage U _dcalso become suddenly large, now have modified the amplitude of modulating wave, make it from U _mbecome U ₂, reduce the amplitude of modulating wave thus make output voltage stabilization.

Said process have adjusted the amplitude of phase voltage, when extraneous conditional mutation, keeps output voltage balance, can superpose triple-frequency harmonics in addition in sinewave modulation signal, thus improve the utilance of bus.Fig. 3 is the modulation signal waveform having superposed triple-frequency harmonics, wherein U _u1represent initial modulating wave, U _u3represent the triple-frequency harmonics composition of superposition, U _urepresenting the modulating wave after superposition triple-frequency harmonics, is saddle ripple.Triple-frequency harmonics is superposed in the sinewave modulation signal of phase voltage, make it to become saddle ripple, after PWM, also triple-frequency harmonics must be comprised in the phase voltage that inverter circuit exports, and phase place is identical, during synthetic thread voltage, triple-frequency harmonics composition is cancelled out each other, it is still sinusoidal wave for exporting, if three-phase voltage is respectively

$U_u=U_m\sin \mathrm{\ωt},U_v=U_m\sin (\mathrm{\ωt}-\frac{2\mathrm{\π}}{3}),U_w=U_m\sin (\mathrm{\ωt}-\frac{4\mathrm{\π}}{3}),$

In above formula, ω t is the angle of getting according to V/F curve, for U _uphase voltage, after injecting triple-frequency harmonics, its expression formula is:

$U_u=\frac{2}{\sqrt{3}}{U}_m(\sin \left(\mathrm{\ωt}\right)+\frac{1}{6}\sin \left(3\mathrm{\ωt}\right))$

For other two phase voltage calculation in like manner.Can find out from above formula, by injecting triple-frequency harmonics, DC bus-bar voltage amplitude is original doubly, bus utilance improves 15%.

Above-described is only the preferred embodiment of the present invention, the invention is not restricted to above embodiment.Be appreciated that the oher improvements and changes that those skilled in the art directly derive without departing from the spirit and concept in the present invention or associate, all should think and be included within protection scope of the present invention.

Claims (2)

1., based on the three-phase output voltage balance adjusting method that phase voltage controls, it is characterized in that, comprise the following steps:

A, every phase DC bus-bar voltage V to high voltage converter _pNsample;

The theory setting value of b, calculating phase voltage:

$V_{\mathrm{PN}\left(\mathrm{mean}\right)}=\frac{1}{n}{\mathrm{\Σ}}_{i=1}^n{V}_{\mathrm{PN}\left(i\right)}---\left(1\right)$

In formula (1), n is power cell number;

Phase voltage amplitude after c, adjustment:

$U_m=V_1^{*}\×\frac{U_{{\mathrm{dc}-\mathrm{rated}}^{*}}}{U_{\mathrm{dc}}}---\left(2\right)$

In formula (2), for the V/f curve of frequency converter, be numerically equal to V _{pN (mean)}, U _dcbe numerically equal to V _pN.

2. as claimed in claim 1 based on the three-phase output voltage balance adjusting method that phase voltage controls, it is characterized in that: the sinewave modulation signal of the phase voltage in described step c after adjustment superposes triple-frequency harmonics.