JPH01311869A - Power factor improving apparatus and electric source using it - Google Patents

Abstract

PURPOSE: To improve power factor by connecting a series LC circuit in series between an apparatus and a power supply and regulating the LC circuit to resonate at a frequency higher than the power supply frequency. CONSTITUTION: A computer system 10 comprises a power supply unit 11 and a load 12 connected therewith. The system 10 is plugged into an AC power supply 13 having an ordinary wire 14 and a wall socket 15 and connected with the socket 15 through a wire 16. The power supply unit 11 comprises a power converter 17 and a power factor compensator 18 interposed between the power converter 17 and the power supply 13 in order to improve the power factor. The compensator 18 connected an inductor and a capacitor in series with the power supply 13 to cause resonance at a frequency higher than the power supply frequency. According to the arrangement, surge current at a high rectifier capacitor is confined automatically within an allowable range at the time of starting an apparatus and a soft start circuit can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for improving the power factor of a power converter and a power supply device using the same.

[Prior Art] In a typical power converter, a rectifier (later called a power regulator), voltage is directly rectified and energy is stored in a large capacitor. This causes narrow, large current pulses to flow from the AC line, thereby causing power factor degradation.

Power factor (P,F,) is desirable as a measure of the efficiency of power passing through a point in a power distribution system.

The power factor is the ratio of the average power (W), that is, the effective power, to the apparent power (VA) flowing into the circuit, and is expressed by the following equation.

P, F, - Actual input power/(input rms voltage x input rms current) Power factor measurements are used in AC power distribution systems where the voltage and current are essentially sinusoidal and typically not in phase. applied to. In such systems, power factor is simply calculated as the cosine of the phase angle between current and voltage (CO5).

Power is distributed most efficiently when the actual power distributed to the load is equal to the product of the input effective voltage and effective current, ie, when the power factor is unity. However, the power factor of power converters is generally less than about 0.75 to 0.5.

Although low power factor can be compensated for by allowing the converter to draw more current to provide sufficient power to the load, problems with low power factor include:

a) Increased impedance loss.

b) The need for AC power distribution system components (eg, circuit breakers, transformers, wiring, etc.) that are larger in capacity and robust enough to withstand the high currents of power converters.

C) The need for larger and more robust rectifier diodes, storage capacitors, and wiring to handle power surges.

d) Greater difficulty and expense in meeting safety standards (e.g. angular laboratories).

These not only increase the cost of the power distribution system, but also increase the cost of the power itself. This is because some users pay not by the actual power consumed but by the apparent power consumed.

For these reasons, it is necessary to improve the power factor of power converters.

As a conventional power factor compensation circuit, Chef Art (W, 5h
This is shown in Chapter 11 of ``Energy Flow and Power Factor in Non-Sinusoidal Circuits'' (Cambridge University Press, 1979) by P. Epherd and P. Zand. Most of them are linear and nonlinear shunt circuits. It cannot be said that these shunt circuits are sufficiently effective in improving the power factor.

Series compensated configurations have also been described, but they are complex, costly, and often contain harmonic frequencies in the rectified load current, such that only the fundamental frequency current must be supplied from the AC line. It is an unreliable active network.

A compensation circuit that avoids the shortcomings of the one proposed by Scheffert and Zandt was proposed by Scholes (G, J. Cales) in Chapter 18 of the Rectifier Circuit Handbook (John Wiley and Sons, 1980). It mentions “adjusted bridge rectifier” and L
A C circuit is provided in series between the AC line and the rectifier and is specifically tuned to resonate at the AC frequency.

However, this circuit has its own serious problems. That is, the problem is that the rectified voltage changes considerably as the load on the rectifier changes. Specifically, it changes by about 30% between no load or light load and normal load (about two degrees). This is a large variation that is unacceptable in most cases. Because of this, at high loads, especially during start-up, overload or short circuits, the voltage and current peaks across both the inductor and capacitor become very large, creating the possibility of damaging the inductor and capacitor. To prevent this, durable and therefore very expensive components must be used that can withstand such surges and avoid breakdown.

Therefore, improving the power factor of the power converter is a more sensible solution.

[Summary of the Invention] The present invention seeks to solve the problems of the prior art described above. According to the present invention, to improve the power factor of devices such as off-line AC line rectifiers that draw power from an AC power source, a series-connected LC circuit is used as a component and the circuit is connected between the device and the power source. The circuit is connected in series between the two, and the circuit is tuned to resonate at a frequency higher than the power supply frequency.

Preferably, the resonant frequency is between 1.4 and 3.5 times the power supply frequency. More preferably, it was about twice the power supply frequency. The experimental formula for determining the desired values of the inductor and capacitor is shown below.

PF: Desired power factor f: Input power frequency (Hz) R double load impedance (Ω) According to the present invention, the effective (RMS) drawn by the device
) The current is reduced, thus improving the power factor of the AC power distribution device and solving or reducing the problems caused by low power factor mentioned above. In particular, the present invention improves the efficiency of AC power equipment;
reducing power losses, particularly in the equivalent series resistance (ESR) of input capacitors, current diodes, line filters and cords; reducing the required capacitance of AC power distribution system components by lowering the peak power requirements of the equipment;
Rectifier diodes of the device, thereby reducing the load
Reduces the cost and required capacity of storage capacitors and wiring. Because whether more stringent safety standards apply generally depends on the maximum effective (RMS) current that can be present in the equipment, improving power factor can easily and inexpensively meet safety standards. Become. The invention also provides protection from inrush currents and short circuit currents.

Furthermore, the present invention improves the power factor without changing component values.
It is suitable for use with a variety of input power frequencies, particularly both 50Hz and 80Hz frequencies. Therefore, the present invention does not require redesign or modification to accommodate different power frequencies in different countries. However, a slight output voltage drop of about 4.5% occurs. The present invention also tends to match the phase of the input current and voltage. In the event of an overload or short circuit, the present invention can automatically limit the current to prevent damage or blown fuses. The invention also automatically limits the value of the inrush current drawn by the large rectifier capacitor during start-up to within an acceptable range, thus eliminating the need for additional soft-start circuits commonly used. Furthermore, since the present invention can be constructed using only passive and well-known components (inductors, capacitors), the structure is simple and reliability is improved.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an example of a system implementing the present invention.

In the figure, one system 10 is composed of a power supply device 11 and a load 12 connected to it. system 10
is a computer system, the load 12 represents the computer itself, and the power supply 11 serves as a power source for driving the computer.

Additionally, system 10 is plugged into an AC power source 13. The power supply 13 has a conventional electrical wire j4 and a wall socket 15, to which the system 10 is plugged by electrical wire 16.

The power supply device 11 is a power converter! Contains a17. Although power converters are conventionally known, in order to provide a sufficient explanation here, an example of a power converter is illustrated in FIG. 2.

The power converter in FIG. 2 consists of a conventional bridge rectifier 21 consisting of four diodes 22, a storage capacitor 23, and a conventional power regulator 24, such as a DC-AC or DC-DC converter. has been done.

The power supply device 11 further includes a power factor compensator 18, which is provided between the power converter 17 and the power source 13 to improve the power factor of the power converter 17 (and therefore of the power supply device 11). Power factor compensator 1
In conventional power supply devices that do not have the power supply 8, it is common to send narrow and very large current pulses from the power supply 13.
By using compensator 18, the width of the current pulse can be substantially widened and the magnitude reduced without significantly affecting the current and voltage phase relationships.

The basic configuration of the compensator 18 is shown in FIG. In the same figure,
Inductor 30 and capacitor 31 are connected in series with power converter 17 and power source 13 . From a safety point of view, the inductor 30 and capacitor 31 are
3 and the power converter 17,
The ground line should be connected as is. However, from a functional point of view, inductor 30 and capacitor 31 may be connected to the ground line, or as shown in FIG.
may be connected to the other.

Furthermore, variations in the basic configuration are possible. That is, a plurality of inductors (70, 71) and capacitors (80, 81)
) can be used to reduce the circuit coupling value of compensator 11 to the coupling value of inductor 30 and capacitor 31 shown in FIG. An example of such a possible configuration is shown in FIG.

In the same figure, one inductor/capacitor 70.8
0 pair is connected in series on the power line between the power supply 13 and the power converter 17, and the other inductor-capacitor 7
1.11 pairs are also connected in series to the ground wire.

Further, another example of the above possible configuration is shown in FIG.

In the same figure, two inductor-capacitor pairs (7
0,80 and 71.81) are connected to one of the tangential lines between the power source 13 and the power converter 17 in parallel with each other.

Each of these LC pairs may be tuned to a different frequency.

As an alternative to the prior art, it is also advantageous to tune the inductor 30 and the capacitor 31, ie to choose their values relative to each other, so that they resonate at a frequency higher than the frequency of the power supply 13. The selected resonant frequency is preferably 1.4 to 3.5 times the power supply frequency. Depending on the weighting of the different parameters, there is a tolerance range for the resonant frequency and therefore for the values of the inductor 30 and capacitor 31.

1) desired amount of power factor improvement; 2) amount of rectified voltage drop due to compensator 18; 3) peak current limit for overload;
4) maximum allowable voltage across capacitor 31; and 5) maximum allowable current through inductor 30.

Experiments have shown that very good results can be obtained with respect to the above parameters at a resonant frequency that is approximately twice the frequency of the power source 13. Since frequencies of 50 Hz and 80 Hz are common for electric i1!13, a resonant frequency of about 110 Hz is advantageous. Inductor 30 and capacitor 3
The experimental formula for determining the desired value of 1 is shown below.

, 238R L ゞ-e I zs x pp ma(7(]A
Nli c2 104. 6jg,pp kuala,,
Fxf PF: Desired power factor f: Power supply frequency (Hz) R: Impedance of the load 12 (Ω) As can be seen from the above formula, the compensator 18 does not need to be a precisely adjusted circuit, and the inductor 30 and capacitor A certain range of values of 31 is allowed and still achieves the original purpose of power factor. Of course, by choosing the inductor and capacitor values within acceptable ranges, the desired power factor (P) can be achieved.

This is slightly lower than the F, ) value. Examples of allowable ranges are ±30% for capacitance values and ±30% for inductance values. This tolerance allows the use of relatively low-cost components in the compensator 18 and allows the interchangeability of a single compensator for both 50 Hz and 80 Hz power systems. Become.

In place of the capacitor 31, a plurality of capacitors connected in parallel or series can also be used. However, from a cost perspective, it is preferable to connect the transformer with a single capacitor to equate the desired capacitance. This configuration is shown in FIG.

As shown in FIG. 7, the primary winding of a transformer 40 is connected in series with the inductor 30 instead of the capacitor 31. Further, the capacitor 41 is connected to both terminals of the secondary winding of the transformer 40. If the transformer 40 is a N transformer, the capacitance of the capacitor 41 is C/N2. Here, C is the capacitance of capacitor 31 replaced by transformer 40 and capacitance 41. The value of N may be greater than 1 in the case of a step-up voltage transformer, and may be smaller than 1 in the case of a Shoryu style transformer.

It would be even more economically advantageous to combine the inductor 30 and transformer 40 shown in FIG. 7 into a single magnetic structure. An example of a compensator] 8 having such a combination structure is shown in FIG.

The structure shown in FIG. 8 uses a transformer 60 with a single folded winding. The input of compensator 18 is connected to the input lead of transformer 60 and one lead of capacitor 41. The output lead of transformer 60 is connected to the other lead of capacitor 41, and the output of compensator 18 is connected to transformer 60.
connected to the tap.

Compensator 18 introduces some voltage drop at the output of converter 17, but there are several ways to compensate for it, if necessary.

One method is to use a transformer 50 as shown in FIG. In this configuration, the output of capacitor 31 is connected to a tap of transformer 50. In addition, the transformer 50
Another method in which one terminal of the winding is connected to the input of the inductor 30 and the other terminal to the return wire or the ground wire is to replace the transformer 50 with an inductor 150 as shown in FIG. It is to use. Inductor 6
0 and 30 are not magnetically coupled. Inductor 6
The inductance of the inductor 30 is larger than that of the inductor 30, for example, about 50 times larger. One terminal of the inductor 60 is the output terminal of the capacitor 31 and the inductor 30
The other terminal is connected to the return line or the ground line.

Note that various modifications and embodiments of the present invention can be considered. For example, a nonlinear inductor could be used to reduce the peak voltage across a capacitor through partial saturation under overload conditions.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram of a system for implementing the present invention, FIG. 2 is a circuit configuration diagram of a power converter in the system shown in FIG. 1, and FIG. 3 is a power converter diagram of the system shown in FIG. 1. A circuit diagram showing a basic configuration of a power factor compensator. FIGS. 4 to 10 are circuit diagrams showing other configuration examples of a power factor compensator. 10: Computer system] 1: Power supply device 17: Power converter 18: Power factor compensator Applicant: American Telephone & FIG.
I FIG, 2 FIG, 3 FNo., 4 FIG,
5 FIO, 7 FIG, 9 FIG, G FIG, 8 FIG-10

Claims (15)

[Claims] (1) In a device for improving the power factor of a rectifier that draws power from an AC power supply of a certain frequency, an inductive means and a capacitive means are connected in series, and a combination of the inductive means and the capacitive means is further provided. is connected in series between the rectifier and the power source, and is adjusted to resonate at a frequency higher than the frequency of the power source. 2. The power factor correction device according to claim 1, wherein said inductive means comprises at least one inductor, and said inductive means comprises at least one capacitor. (3) said capacitive means comprises a transformer having a primary winding connected in series between said rectifier and said power supply and further a secondary winding; connected in parallel to said secondary winding; The power factor correction device according to claim 1, further comprising: a capacitor; 4. The power factor correction device of claim 3, wherein said transformer and said inductive means are contained within a single magnetic structure. (5) a second connected in series with said capacitive means and in parallel with said inductive means and rectifier combination;
The power factor correction device according to claim 1, further comprising inductive means. (6) further comprising a transformer having a winding connected in parallel with the combination of said inductive means and rectifier and having a tap connected to said capacitive means, a portion of said winding being connected to said capacitive means; 2. A power factor correction device according to claim 1, characterized in that the device is connected in series between the means and the inductive means. (7) The capacitive means has a capacitance (104/R×f)e^-^6.38^×^P^F farad ±30%, and the inductive means has an inductance (238R/f)e^ 12.8＾×＾P＾F microhenry ±30%, where PF is the desired value of power factor, f is the frequency of the above current source (Hz), and R is the load impedance on the output of the above rectifier (Ω) It is. The power factor improvement device according to claim 1, characterized in that it has: (8) The above resonance frequency is 1.4 to 3 of the above power supply frequency.
．． 2. The power factor correction device according to claim 1, wherein the power factor correction device is within a range of 5 times. (9) The power factor correction device according to claim 8, wherein the resonance frequency is twice the power supply frequency. (10) The capacitive means has a capacitance of (104/R×f)e^-^6.38^×^F farads ±30%, and the inductive means has a capacitance of (238R/f)e^ It has an inductance of 12.8＾＾＾P＾F microhenry ±30%, where PF is the desired value of power factor, f is the frequency (Hz) of said current source, and R is the load on the output of said rectifier. Impedance (Ω). The power factor correction device according to claim 8, characterized in that: (11) a circuit consisting of means for connecting to an alternating current power supply of a certain frequency; means connected to the connecting means and rectifying the alternating current; and inductive means and capacitive means connected in series with each other; 1. A power supply device, characterized in that the circuit is interposed in series between the connecting means and the rectifying means, and is adjusted to resonate at a frequency higher than the alternating current frequency. (12) The capacitive means has a capacitance of (104/R×f)e^-^6.38^×^F farads ±30%, and the inductive means has a capacitance of (238R/f)e^ It has an inductance of 12.8＾＾＾P＾F microhenry ±30%, where PF is the desired value of power factor, f is the frequency (Hz) of said current source, and R is the load on the output of said rectifier. Impedance (Ω). The power supply device according to claim 11, characterized in that: (13) The above resonant frequency is 1.4 to 1.4 of the above power supply frequency.
12. The power supply device according to claim 11, wherein the power supply is within a range of 3.5 times. (14) The power supply device according to claim 13, wherein the resonant frequency is twice the power supply frequency. (15) The capacitive means has a capacitance of (104/R×f)e^-^6.38^×^F farads ±30%, and the inductive means has a capacitance of (238R/f)e^ It has an inductance of 12.8＾＾＾P＾F microhenry ±30%, where PF is the desired value of power factor, f is the frequency (Hz) of said current source, and R is the load on the output of said rectifier. Impedance (Ω). The power supply device according to claim 13, characterized in that: