GB2348519A

GB2348519A - Compensating converter output power factor

Info

Publication number: GB2348519A
Application number: GB9918624A
Authority: GB
Inventors: Gavin Chang; Jing Chen
Original assignee: Delta Electronics Inc
Current assignee: Delta Electronics Inc
Priority date: 1999-03-31
Filing date: 1999-08-09
Publication date: 2000-10-04
Anticipated expiration: 2019-08-09
Also published as: GB9918624D0; GB2348519A8; CN1251389C; CN1270440A; GB2348519B

Abstract

A system for eliminating harmonics and compensating the power factor of a frequency converter, uses a resistor 21 at the input side of an inverter 12 to derive values for positive and negative peak currents. These values are compared and combined to produce an estimate of the inverter output current. This estimate is used together with measured values of the load voltage and the inverter input voltage and current to calculate a compensating factor to be applied to the converter output waveform.

Description

METHOD FOR COMPENSATING SIGNAL The present invention relates to a method for compensating a signal outputted from an electronic device, e. g. a converter.

Please refer to Fig. 1 which is a circuit diagram of a frequency converter of the prior art. The frequency converter includes a power source 15, an alternating-current/direct-current (AC/DC) converter 11, a direct-current/alternating-current (DC/AC) converter 12, and a current sensor 14. The output signal of the frequency converter is an alternating-current signal and is outputted to a load 13. The DC/AC converter 12 includes a plurality of switching circuits which will generate many harmonic waves and in turn adversely affect the characteristics of the power signal, i. e. the power factor. The power factor is a ratio of the actual power to apparent power (simple product of voltage and current). The power factor p can be calculated from an equation of p = cos 0, where 0 is the phase angle of the signal. In order to maintain the current's stability of the load 13, the harmonic waves should be eliminated and a method for compensating the signal according to the power factor is needed. Therefore, in order to estimate a compensating factor of the signal, the signal outputted from the DC/AC converter 12 is measured by the current sensor 14 and then transmitted to a circuit, e. g. a microprocessor, for processing and compensating the signal.

The current sensor 14 positioned at the alternating-current end of the DC/AC converter 12 must have an ability for loading large electric powers. However, the current sensor 14, e. g. current transformer (CT), is relatively expensive. In order to reduce the cost of the converter, the current sensor 14 is removed and the method for estimating the compensating factor should be changed.

Because the switching circuits inside the DC/AC converter 12 will affect the power signal, the output current transmitted to the load can be estimated by the input current of the DC/AC converter 12. Please refer to Fig. 2 which shows the circuit of another frequency converter of the prior art. A resistor 21 is placed at the direct-current end of the DC/AC converter 12 as shown in Fig. 2. The resistor 21 is used as a feedback device for compensating the output signal of the DC/AC converter. The signal is compensated according to the phase angle of the output signal, a compensating factor is then calculated. The compensating factor for compensating the output signal of the DC/AC converter is estimated according to the signal passing through the resistor 21. This compensating method is a dead-time compensation.

Please refer to Fig. 3 which shows the circuit used in the dead-time compensation of the prior art. The voltage difference of the resistor 21 is measured and then transformed to a current signal. The current signal is amplified by a preamplifier 31 and then divided into a positive peak signal and a negative peak signal. The positive peak current Ipeak (+) and negative peak current Ripez (-) are respectively measured by the positive peak current detector 32 and the negative peak current detector 33. (-) are compared by a comparator 34. The relatively ak (+) and peak (-) is defined as an estimated output current and then outputted to a microprocessor 35 for calculating the compensating factor of the dead-time compensation.

Please refer to Fig. 4 which is a flow chart showing the method for compensating the signal. First, the standard voltage V. of the load is defined and the input voltage V, and input current li of the DC/AC converter are also measured. Thereafter, the positive peak current Ipeak (+) and the positive peak current Ip (-) of the feedback device, i. e. the resistor, are measured. The relatively larger one of Ripez (+) and I (-) is defined as an estimated output current Io. The compensating factor d for compensating the output signal is calculated by an equation of d = cos

The output current of the DC/AC converter 12 is adjusted according to the compensating factor d.

However, the waveform of the signal outputted from the DC/AC converter 12 is varied along with different phase angles. Please refer to Figs. 5 (a)-5 (c) which show different waveforms with different phase angles. Figs. 5 (a), 5 (b), 5 (c) are diagrams respectively show the waveform of the output signal having a phase angle of 30,60,90 degree.

The waveform of the output signal is changed when the phase angle is greater than 30 degree because the estimated output current Io i. e. the relatively larger one of lpeak (+) and Ipeak (-), is not the same as the actual output current. In fact, when the phase angle is greater than 60 degree, the estimated output current Io is smaller than the actual output current.

Therefore, the compensating factor d calculated by the estimated output current Io is not correct, and this method for compensating the output signal is poor. Besides, the estimated output current Io is also smaller than the actual one when the phase angle is ranged from 30 to 60 degree.

It is not easy to calculate an estimated output current which approaches to the actual current unless the current is measured by a detector with a high sensitivity. However, the detector with a high sensitivity is very expensive and the cost of the converter will be increased.

Referring to Fig. 6, the form of the output current with poor compensation is not smooth and will cause a damage of the load. The operation of the load is very unstable. Therefore, it is tried by the applicant to solve the above-described problem.

Therefore, an object of the present invention is to provide a method for estimating a compensating factor for compensating a signal.

Another object of the present invention is to provide a method for estimating a compensating factor used in a dead-time compensation.

According to the present invention, the method for compensating an output signal of an electronic device which has an input end electrically connected to a feedback device and an output end electrically connected to a load, includes the steps of (a) measuring a standard voltage Vo of the load, (b) determining an input voltage Vi and an input current li of the electronic device, and (c) generating a feedback signal based on the input voltage Vj. The method further includes steps of (d) determining a maximum current ImaX and a minimum current Iminof the feedback signal passing through the feedback device, (e) defining an estimated output current Io of the electronic device based on the maximum current Imaxand the minimum current Imjn, and (f) compensating the output signal of the electronic device according to a compensating factor d determined by the standard voltage Vu'té input voltage Vj, the input current li, and the estimated output current Io of the electronic device.

Preferably, the electronic device is a DC/AC converter coupled to a AC/DC converter. Besides, the feedback device includes a resistor electrically connected between the AC/DC converter and the DC/AC converter for generating a voltage difference in order to estimate a current of the feedback signal.

In accordance with the present invention, the feedback signal is amplified by an amplifier of the feedback device and then divided into a positive peak signal and a negative peak signal. The currents of the positive peak signal and the positive peak signal are respectively detected by a positive peak current detector and a negative peak current detector. The maximum current ImaX is the relatively larger one detected by the positive peak current detector and the negative peak current detector. The minimum current Imin is the relatively smaller one detected by the positive peak current detector and the negative peak current detector.

In accordance with the present invention, the estimated output current Io is calculated according to the maximum current Imax and the minimum current Iman boy a first equation of Io=ImaX+kImjn where k is a constant.

In accordance with the present invention, the compensating factor d is determined by a second equation d = cos

where Vo is the standard voltage of the load, V ; is the input voltage, li is the input current, and Io is the estimated output current of the electronic device.

In accordance with the present invention, the method is applied in compensating a signal of a frequency converter. Besides, the method is a dead-time compensation.

The present invention may best be understood through the following description with reference to the accompanying drawings, in which: Fig. 1 is a diagram showing a conventional circuit of a frequency converter; Fig. 2 is a diagram showing another conventional circuit of a frequency converter; Fig. 3 is a diagram showing the devices used for a dead-time compensation of a prior art; Fig. 4 is a flow chart illustrating the method for compensating a signal according to a prior art; Fig. 5 is a schematic diagram showing the waveforms of the signals having different phase angles in the prior art; Fig. 6 is a schematic diagram showing the form of the current with poor compensation in the prior art; Fig. 7 is a schematic diagram showing the circuits used in the deadtime compensation according to the present invention; Fig. 8 is a flow chart showing the method for compensation a signal in the present invention; Fig. 9 is a schematic diagram showing the form of the current after compensation according to the present invention; Fig. 10 is a schematic diagram showing the circuit of the preamplifier according to the present invention; and Fig. 11 is a diagram showing the circuits of the positive peak current detector and negative peak current detector according to the present invention.

Please refer to Fig. 7 which shows the feedback device for estimating a compensating factor used in the dead-time compensation according to the present invention. The feedback device includes a resistor 21, a preamplifier 31, a positive peak current detector 32, a negative peak current detector 33, and a microprocessor 35. The voltage difference of the resistor 21 is measured and then transformed to a current signal. The current signal is amplified by a preamplifier 31 and then divided into a positive peak signal and a negative peak signal.

The currents Ipeak (+) and Ipe, k (-) of the positive peak signal and the negative peak signal are respectively measured by the positive peak current detector 32 and the negative peak current detector 33. In the microprocessor 35, an estimated output current Io is estimated and then a compensating factor of the dead-time compensation is calculated.

Referring to Fig. 8 which is a flow chart showing the method for compensating the output signal of a DC/AC converter by the compensating factor according to the present invention. The standard voltage Vo outputted from the DC/AC converter is defined first. The input voltage Vi and input current li of the DC/AC converter are then measured. Then, the positive peak current Ipeak (+) and the positive peak current Ipeak (-) of the feedback device are measured. The relatively larger one of the Ipg (+) and Ipeak (-) is defined as and the relatively smaller one of the Ipeak (+) and Y (-) is defined as in. The estimated output current Io of the converter depends on both of ImaX and Imjn. The estimated output current Io is estimated by a first equation of Io=Imax + min where k is a constant. The compensating factor d for compensating the signal is then calculated by a second equation of d=cos

Finally, the output current of the DC/AC converter is compensated according to the compensating factor d.

In the prior art, the maximal peak current Imax is directly defined as the estimated output signal Io. Under such circumstance, the estimated output current Io should be the same as the actual output current.

However, for the DC/AC converter having a phase angle of 90 degree, the peak current of the input signal is 0.886 times smaller than the actual output current. The estimated output current is smaller than the actual output current in this case. On the contrary, the estimated output current is the same with the actual output current by using the first equation according to the present invention. When the phase angle is 90 degree, the first equation becomes 0.866+0.866k=l. The k value can be calculated from the first equation; therefore, k is 0.1547. The k value is varied with the phase angle, but the difference is small.

Therefore, k can be defined as a constant, that is, k is 0.1547.

By the method described in the present invention, the estimated output currents will be approached to the actual output currents having different phase angles, especially when the phase angles are ranged from 60 to 90 degree. Because the estimated phase angle calculated by the second equation will be similar to the actual phase angle, the form of the signal after the compensation is very smooth as shown in Fig. 9.

Please refer to Fig. 10 which is a diagram showing the circuit of the preamplifier 31. In addition, Fig. 11 is a diagram showing the circuits of the positive peak current detector 32 and negative peak current detector 33 in the present invention. The circuits have various modifications and can be easily made by those skilled in the art, so there is no further description of these circuits.

In the present invention, the output current of the frequency converter can be estimated precisely. Two peak currents Ipeak (+) and Ipe (-) of the input signal are measured. In the method for compensating a signal according to the present invention, the estimated output current is not calculated directly from the relatively lager one of the peak currents. The relatively larger one of the Ripez (+) and Ipeak (-) is defined as Imax and the relatively smaller one of the Ipea"(+) and Ipeak (-) is defined as Iman. The estimated output current Io is then calculated by an equation Io=Im"+ kImjn where k is a constant. Therefore, the estimated output current is very similar to the actual output current. The compensating factor d for compensating the output signal of the converter is then calculated from the standard output voltage VOS the input voltage Vj, the input current Ij, and the estimated output current Io by a second equation d = cos

Therefore, the output signal after compensated by the compensating factor is very similar to the actual output signal.

Claims

CLAIMS: 1. A method for compensating an output signal of an electronic device, wherein said electronic device includes an input end electrically connected to a feedback device and an output end electrically connected to a load, comprising steps of : (a) measuring a standard voltage Vo of said load; (b) determining an input voltage V ; and an input current li of said electronic device; (c) generating a feedback signal based on said input voltage Vi ; (d) determining a maximum current ImaX and a minimum current 1 of said feedback signal passing through said feedback device; (e) defining an estimated output current Io of said electronic device based on said maximum current Im and said minimum current Imin ; and (f) compensating said output signal of said electronic device according to a compensating factor d determined by said standard voltage Vu, raid input voltage Vj, said input current li, and said estimated output current Io of said electronic device.

2. The method according to claim 1 wherein said electronic device is a DC/AC converter coupled to an AC/DC converter.

3. The method according to claim 2 wherein said feedback device comprises a resistor electrically connected between said AC/DC converter and said DC/AC converter for generating a voltage difference in order to estimate a current of said feedback signal.

4. The method according to claim 3 wherein said feedback signal is amplified by an amplifier of said feedback device and then divided into a positive peak signal and a negative peak signal.

5. The method according to claim 4 wherein currents of said positive peak signal and said positive peak signal are respectively detected by a positive peak current detector and a negative peak current detector.

6. The method according to claim 5 wherein said maximum current ImaX is the relatively larger one detected by said positive peak current detector and said negative peak current detector.

7. The method according to claim 6 wherein said minimum current Iman ils the relatively smaller one detected by said positive peak current detector and said negative peak current detector.

8. The method according to claim 1 wherein said estimated output current Io is calculated according to said maximum current Imax and said minimum current Imjn by a first equation of Io=Imaxmin where k is a constant.

9. The method according to claim 1 wherein said compensating factor d is determined by a second equation d = cos

where Vo is said standard voltage of said ! oad, V, is said input voltage, li is said input current, and Io is said estimated output current of said electronic device.

10. The method according to claim 1 wherein said method is applied in compensating a signal of a frequency converter.

11. The method according to claim 1 wherein said method is a dead-time compensation.

12. A method for determining a compensating factor for compensating an output signal of a converter, wherein said converter has an input end electrically connected to a feedback device and an output end electrically connected to a load, comprising steps of : (a) measuring a standard voltage Vo of said load ; (b) determining an input voltage Vi and an input current li of said converter; (c) generating a feedback signal based on said input voltage Vj ; (d) determining a maximum current Imax and a minimum current Imjn of said feedback signal passing through said feedback device; (e) defining an estimated output current Io of said converter based on said maximum current ImaX and said minimum current Iman ; and (f) calculating said compensating factor d according to said standard voltage Vu, raid input voltage Vj, said input current li, and said estimated output current Io.

13. The method according to claim 12 wherein said estimated output current Io of said converter is calculated according to said maximum current Imax and said minimum current Imjn by a first equation of I. =lmax+klmin where k is a constant.

14. The method according to claim 12 wherein said compensating factor d is determined by a second equation d = cos

where Vo is said standard voltage of said load, Vi is said input voltage, I ; is said input current, and Io is said estimated output current of said converter.

14. A method for compensating an output signal as herein before described with reference to Figs. 7 to 11 of the accompanying drawings.

Amendments to the claims have been filed as follows CLAIMS : 1. A method of compensating the power of an output signal of an electronic device, wherein said electronic device includes an input end electrically connected to a feedback device and an output end electrically connected to a load, comprising steps of : (a) defining an output voltage Vo of said load; (b) determining an input voltage V ; and an input current I, of said electronic device; (c) generating a feedback signal based on said input voltage Vi ; (d) determining a maximum current Imax and a minimum current Imin of said feedback signal passing through said feedback device; (e) defining an estimated output current Io of said electronic device based on said maximum current ImaX and said minimum current Imin, and (f) compensating said output signal of said electronic device according to a compensating factor d determined by said output voltage VOX said input voltage V ;, said input current Ii, and said estimated output signal Io of said electronic device.
2. The method according to claim 1 wherein said electronic device is a DC/AC converter coupled to an AC/DC converter.
3. The method according to claim 2 wherein said feedback device comprises a resistor electrically connected between said AC/DC converter and said DC/AC converter for generating a voltage difference in order to estimate a current of said feedback signal.
4. The method according to claim 3 wherein said feedback signal is amplified by an amplifier of said feedback device and then divided into a positive peak signal and a negative peak signal.
5. The method according to claim 4 wherein currents of said positive peak signal and said positive peak signal are respectively detected by a positive peak current detector and a negative peak current detector.
6. The method according to claim 5 wherein said maximum current Imx is the relatively larger one detected by said positive peak current detector and said negative peak current detector.
7. The method according to claim 6 wherein said minimum current Iman ils the relatively smaller one detected by said positive peak current detector and said negative peak current detector.
8. The method according to claim 1 wherein said estimated output current Io is calculated according to said maximum current Ima and said minimum current Imjn by a first equation of Io=Ima, +kImjn where k is a constant.
9. The method according to claim 1 wherein said compensating factor d is determined by a second equation d = cos

where Vo is said standard voltage of said load, V is said input voltage, Ii is said input current, and Io is said estimated output current of said electronic device.
10. The method according to claim 1 wherein said method is applied in compensating a signal of a frequency converter.
11. The method according to claim 1 wherein said method is a dead-time compensation.
12. A method for determining a compensating factor d for compensating the power of an output signal of a converter, wherein said converter has an input end electrically connected to a feed back device and an output end electrically connected to a load, comprising steps of : (a) defining an output voltage V. of said load; (b) determining an input voltage Vi and an input current I, of said converter; (c) generating a feedback signal based on said input voltage Vi ; (d) determining a maximum current I, and a minimum current inof of said feedback singal passing though said feedback device; (e) defining an estimated output signal I. of said converter based on said maximum current I",., and said minimum current Iman ; and (f) calculating said compensating factor d according to said output voltage V., said input voltage Vj, said input current said estimated output current Io of said converter for compensating said power of said outp signal of said vonverter according to said compensating factor d.
13. The method according to claim 12 wherein said estimated output current Io of said converter is calculated according to said maximum current Im"and said minimum current Imjn by a first equation of Io=Imax+kImin where k is a constant.
14. A method for compensating an output signal as herein before described with reference to Figs. 7 to 11 of the accompanying drawings.

14. The method according to claim 12 wherein said compensating factor d is determined by a second equation d = cos

where Vo is said output voltage of said load, Vj is said input voltage, I ; is said input current, and Io is said estimated output current of said converter.