JPH053678A - Dc/ac power supply - Google Patents

Abstract

PURPOSE:To restrict peak factor of current being fed from a DC power supply regardless of fluctuation of AC load by providing a voltage control means for outputting a current reference corresponding with a voltage difference and for varying the limit value of current reference, and means for controlling the current being fed from the DC power supply. CONSTITUTION:A voltage control section 12 compares the voltage Vd of a capacitor 7 detected at a voltage detecting section 16 with a reference voltage VR and outputs a current reference I'. A current control section 25 compares the output current id from a diode bridge 5 detected through a current detector 29 with the current reference I'd and a PWM control section 15 controls MOSFETs 3, 4 to reduce current difference. A limiter 24 limits the output value of the voltage control section 12 and when the current reference I'd exceeds an input signal (f) to the limiter 24, input to the voltage control section 12 is offset to limit the I'd to the value of (f). A function unit 23 outputs a current limit signal (f) corresponding with the difference between the reference voltage VR and a voltage Vdx detected at the voltage detecting section 16, and the current limit signal (f) is fed to the limiter 24.

Description

Detailed Description of the Invention

 [Object of the Invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / AC power supply device improved to efficiently obtain an AC power supply from a DC power supply.

[0002]

2. Description of the Related Art A device for obtaining an AC power source from a DC power source such as a battery is used as an uninterruptible power supply (UPS) for a computer.
There is an increasing demand to use general household appliances by obtaining AC 100V from C12V or 24V). The configuration of a conventional DC / AC power supply device of this type is shown in FIG. 5, and its operation will be described.

In FIG. 5, a DC power source 1 is added to the center tap of a transformer 2 and one ends of MOSFETs 3 and 4,
By alternatingly switching the MOSFETs 3 and 4, alternating high frequency power is supplied to the primary side of the transformer 2.

The secondary side voltage of the transformer 2 is rectified by the diode bridge 5, and a second DC voltage smoothed by the reactor 6 and the capacitor 7 is obtained. This second DC voltage is PWM-controlled by the inverter bridge 8 and output in a waveform close to a sine wave, and an AC output from which harmonics are removed by the reactor 9 and the capacitor 10 is obtained. In addition, the inverter control unit 22 uses the P of the inverter bridge 8.
Although WM control is performed, it is not directly related to the present invention, and therefore detailed description thereof is omitted.

[0005] Voltage controller 12, voltage detector 16 as a voltage difference over the voltage V _d is compared with a constant reference voltage V _R PWM controller 15 of the capacitor 7 detected decreases in MOSFET 3, Control 4

The current limiting section 20 compares the output current I _ax of the transformer 2 detected via the current transformer 18 and the diode 19 with the current limiting value I _L, and when the current is a predetermined current or more, the PWM controlling section 15 Limit the input signal to limit the output current I _ax .

FIG. 6 shows the waveform of each part when this conventional device is supplying power to a load having a power factor of 100%. In this case, when the AC output voltage V _a and the output current I _a are in phase and a single-phase AC output is obtained, the instantaneous power P (t) is sin ² It becomes a function of (wt) and becomes (1-cos2wt) / 2 as shown in P _a of FIG.
Becomes the waveform of. The control shown in FIG. 5 is generally adopted in a DC / DC converter, and the left side of the diode bridge 5 is regarded as a voltage source.

In such control, the instantaneous power of the load is shown in FIG.
When it is generated like the waveform of P _a , a current having a similar waveform such as i _DC is made to flow from the DC power supply 1 and the DC voltage V _d is controlled so that it hardly changes. Since the load of a general DC / DC converter is direct current, the fluctuation of the instantaneous power is small and the conventional method has no problem.

[0009]

However, in the DC / AC power supply device, since the AC output is an AC output, the instantaneous power of the load changes, and the variable power becomes maximum at a power factor of 100%.

When i _DC fluctuates and flows in order to supply this fluctuating power from the DC power supply 1, the effective value with respect to the average value, that is, the waveform rate becomes large and the power loss increases. When the effective current of i _DC is i _rms , the loss (mainly copper loss) is proportional to i ² _rms, and is the square rate of the waveform ratio with respect to the loss at smooth DC.

For example, in the full-wave rectified waveform, the waveform ratio is 1.1, so the loss increases by about 20% with respect to the smooth DC.
In the half-wave rectified waveform, the waveform ratio is 2.2, and the loss is about 5 times. Since the iDC waveform in FIG. 6 is close to a half-wave rectified waveform, the loss is about 5 times. For this reason, the conventional device of FIG. 5, which uses the control system of the DC / DC converter for the DC / AC power supply device, has a drawback that the efficiency is lowered by 4 to 5%.

The present invention has been made in view of the above problems, and its object is to prevent the crest factor of the current supplied from the DC power supply from increasing even when the instantaneous power of the AC load changes. An object of the present invention is to provide a highly efficient DC / AC power supply device that is controlled to reduce loss. [Constitution of Invention]

[0013]

In order to achieve the above object, the present invention comprises a chopper means for converting the voltage of a DC power supply into a high frequency voltage and supplying the high frequency voltage to the primary side of the transformer. In a device in which a high frequency voltage on the secondary side is rectified to obtain a second direct current voltage and a single-phase alternating current voltage is obtained from the second direct current voltage, the second direct current voltage is compared with a reference voltage. A voltage control unit that outputs a current reference according to the voltage deviation and changes the limit value of the current reference according to the voltage deviation, and a current that controls the current supplied from the DC power supply according to the current reference. A DC / AC power supply device is configured by providing control means.

[0014]

With the above configuration, when the voltage deviation is small, the current limit value is small, and when the voltage deviation is large, the current limit value is increased, and the current is supplied from the DC power supply according to the current reference. The vicinity of the peak of the current is limited to the current limit value. Due to this action, the waveform ratio of the current is controlled to be small and the loss is reduced.

[0015]

FIG. 1 shows an embodiment of the present invention. The same parts as those in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted. In FIG. 1, the voltage control unit 12 compares the voltage V _{d of the} capacitor 7 detected by the voltage detection unit 16 with the reference voltage V _R and compares the current reference I _d ^*. Is output.

The current controller 25 detects the output current i _d of the diode bridge 5 detected by the current detector 29 and the current reference I _d.
^* PWM control section 15 in the direction of decreasing the current deviation
The MOSFETs 3 and 4 are PWM-controlled via.

The limiter 24 limits the output value of the voltage controller 12, and the current reference I _d ^*. Exceeds the signal f input to the limiter 24, the input of the voltage control unit 12 is canceled and I _d ^* Is limited to the value of signal f. The function unit 23 outputs the current limiting signal f as shown in FIG. 2 according to the deviation value between the reference voltage V _R and the detection voltage V _dx by the voltage detection unit 16 and inputs it to the limiter 24.

With the above configuration, the current reference I _d ^* is set according to the deviation value of V _R -V _dx ^. Is limited, and the current limit value is small when the deviation value is small under a light load, and the current limit value is large when the deviation value is large under a heavy load. As a result, the energization width of Idc acts so as to broaden as shown in FIG.

That is, the instantaneous electric power P _a of the AC output is shown in FIG.
Although it fluctuates greatly as shown in, power is supplied mainly from the capacitor 7 near the peak of the power, and the DC power supply 1
The current i _DC supplied from is limited near the peak of power (thick line portion). By this action, the waveform ratio of i _DC can be made small (1.1 or less) regardless of whether the load is light or heavy.

According to this embodiment, the peak value of the current i _DC is limited and the waveform ratio is controlled to be small even if the response of the voltage control is accelerated, and the resistance loss is reduced to ¼ to ⅕, It is possible to provide an efficient DC / AC power supply device. The present invention can be modified into the configuration of the second embodiment shown in FIG.

In FIG. 4, the proportional amplifier 30 proportionally amplifies the deviation value between the reference voltage V _R and the detection voltage V _dx of the capacitor 7 and outputs the error voltage ΔV. The control amplifier 12 has a proportional-integral amplification function, and its output I _d ^* Is limited to the value of the current limit value f by the limiter 24. The function unit 23 outputs the function value f as shown in FIG. 2 with the error voltage ΔV as the input deviation value and operates with the function value f as the current limit value. As a result, the same effect as in the case of FIG. 1 can be obtained. In the above explanation,
Although the example in which the output current of the diode bridge 5 is detected has been shown, the current on the secondary side or the primary side of the transformer 2 may be detected.

[0022]

According to the present invention, in the DC / AC power supply device in which the instantaneous power supplied to the load fluctuates, the waveform rate of the current supplied from the DC power supply side can be suppressed to a small value.
It is possible to provide a DC / AC power supply device with reduced loss and improved efficiency.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment according to the present invention.

FIG. 2 is a characteristic diagram of a function unit 23 according to the first embodiment.

FIG. 3 is a waveform diagram for explaining the operation of the first embodiment.

FIG. 4 is a configuration diagram of a main part of a second embodiment according to the present invention.

FIG. 5 is a configuration diagram of a conventional device.

FIG. 6 is a waveform diagram for explaining problems of the conventional device.

[Explanation of symbols]

1 ... DC power supply, 2 ... transformer, 3, 4 ... MOSFET, 5
... diode bridge, 6 ... reactor, 7 ... capacitor, 8 ... inverter bridge, 12 ... voltage controller, 15
... PWM control section, 16 ... Voltage detection section, 22 ... Inverter control section, 23 ... Function unit, 24 ... Limiter, 25 ... Current control section, 27 ... Current detector, 30 ... Proportional amplifier.

Claims (1)

Claim: What is claimed is: 1. A chopper means for converting the voltage of a DC power supply into a high frequency voltage and supplying the high frequency voltage to the primary side of the transformer, and rectifying the high frequency voltage on the secondary side of the transformer. In a device that obtains a DC voltage of 2 and obtains a single-phase AC voltage from the second DC voltage, compares the second DC voltage with a reference voltage and outputs a current reference according to a voltage deviation. A DC control means for controlling a current supplied from the DC power supply according to the current reference, and a voltage control means for changing a limit value of the current reference according to the voltage deviation. / AC power supply.