JP3015512B2 - DC / AC power supply - Google Patents

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 improved to efficiently obtain an AC power from a DC power supply.

[0002]

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

In FIG. 5, a DC power supply 1 is applied to a center tap of a transformer 2 and one ends of MOSFETs 3 and 4.
By switching the MOSFETs 3 and 4 alternately, AC high frequency power is supplied to the primary side of the transformer 2.

The secondary 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 is output in a waveform close to a sine wave, and an AC output from which harmonics have been removed by the reactor 9 and the capacitor 10 is obtained. Note that the inverter control unit 22 determines the P of the inverter bridge 8.
Although the WM control is performed, since it is not directly related to the present invention, the detailed description 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, 4 is controlled.

[0006] Current limiting unit 20, current transformer 18, when more than a predetermined current by comparing the output current I _ax and the current limit value I _L of the transformer 2 detected via the diode 19 of the PWM control unit 15 The input signal is limited to limit the output current _Iax .

FIG. 6 shows waveforms at various points when the conventional device supplies power to a load having a power factor of 100%. In this case, when the output voltage V _a and the output current I _a of the single-phase AC output in-phase AC, the instantaneous power P (t) is sin ² As shown in P _a function and becomes Figure 2 (wt) (1-cos2wt) / 2
Waveform. The control shown in FIG. 5 is a method generally employed in a DC / DC converter, and is such that the left side of the diode bridge 5 is regarded as a voltage source.

In such a control, the instantaneous power of the load is reduced as shown in FIG.
The DC voltage V _d to flow a current of similar waveform as the P _a of i _DC and generated from the DC power source 1 as shown in a waveform is controlled not substantially change. Since the load of a general DC / DC converter is direct current, the instantaneous power fluctuates little and there is no problem in the conventional method.

[0009]

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

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

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

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to prevent the crest factor of a current supplied from a DC power supply from increasing even when the instantaneous power of an AC load fluctuates. It is an object of the present invention to provide a DC / AC power supply having high efficiency by controlling loss. [Configuration of the Invention]

[0013]

To achieve the above object of the Invention The invention according to claim 1, chopper means for supplying to the primary side of the transformer converts the voltage of the DC power supply to the high frequency voltage
Rectifying means for rectifying a high-frequency voltage on the secondary side of the transformer
And a device configured to obtain a single-phase AC voltage from the second DC voltage rectified through the rectifier .
Outputs a current reference in accordance with the voltage deviation by comparing the second DC voltage and the reference voltage, depending on the voltage deviation
And voltage control means for limiting values of the current reference is changed, the
Current reference from voltage control means and output current of said rectification means
Current that outputs a control signal according to the current deviation
Control means and a control signal from the current control means.
The chopper means in a direction in which the current deviation decreases.
Chopper control means for controlling
You . Further, the invention according to claim 2 increases the voltage of the DC power supply.
Chopper that converts to frequency voltage and supplies it to the primary side of the transformer
Means for rectifying the high frequency voltage on the secondary side of the transformer
And a second rectified through the rectifying means.
In a device that obtains a single-phase AC voltage from a DC voltage
And comparing the second DC voltage with a reference voltage to determine a voltage deviation.
Outputs a current reference according to the voltage deviation, and responds to the voltage deviation.
Voltage control means in which the current reference limit value changes,
The current reference from this voltage control means and the secondary side of the transformer
And outputs a control signal according to the current deviation.
Current control means and a control signal from the current control means.
The chopper in a direction in which the current deviation decreases.
Chopper control means for controlling the means.
And Further, the invention according to claim 3 is characterized in that the voltage of the DC power supply
Is converted to a high-frequency voltage and supplied to the primary side of the transformer.
Rectifier means and a high frequency voltage on the secondary side of the transformer.
Rectifying means, and the rectifying means rectified through the rectifying means.
2 to obtain a single-phase AC voltage from the DC voltage
And comparing the second DC voltage with a reference voltage.
The current reference is output according to the deviation, and the voltage deviation is output.
Voltage control means for changing the limit value of the current reference according to
And the current reference from the voltage control means and one of the transformers.
Outputs a control signal according to the current deviation by comparing the
A current control means for force control signal from the current control means
Signal to reduce the current deviation.
Chopper control means for controlling the chopper means.
Features.

[0014]

According to the above construction, 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. 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. By this effect, 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 denoted by the same reference numerals, and description thereof is omitted. In Figure 1, the current reference voltage control unit 12 compares the voltage V _d and the reference voltage V _R of the capacitor 7 detected by the voltage detector 16 I _d ^* Is output.

The output current of the current control unit 25 is a diode bridge 5 which is detected by the current detector 29 i _d and the current reference I _d
^* And the PWM control unit 15 in the direction in which the current deviation decreases.
Control the MOSFETs 3 and 4 via the PWM.

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 controller 12 is canceled, and I _d ^* To the value of the signal f. The function unit 23 outputs a current limiting signal f as shown in FIG. 2 according to a deviation value between the reference voltage V _R and the detection voltage V _dx detected by the voltage detection unit 16 and inputs the current limiting signal f to the limiter 24.

With the above configuration, the current reference I _d ^{* is} determined according to the deviation value of V _R -V _dx ^. Is limited, 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 width of the current flowing through Idc acts to widen as shown in FIG.

[0019] That is, the instantaneous power P _a of the AC output 3
As shown in FIG. 5, the power is mainly supplied from the capacitor 7 near the peak of the power,
Current i _DC supplied from the vicinity of the power peak of the (thick line portion) is restricted. With this operation, the waveform ratio of i _DC can be reduced (1.1 or less) regardless of the load.

According to this embodiment, even if the response of the voltage control is accelerated, the peak value of the current i _DC is limited, the waveform ratio is controlled to be small, the resistance loss is reduced to ４ to ５, and An efficient DC / AC power supply can be provided. The present invention can be modified to the structure of the second embodiment shown in FIG.

In FIG. 4, a proportional amplifier 30 proportionally amplifies a deviation value between a reference voltage V _R and a detection voltage V _dx of a capacitor 7, and outputs an error voltage ΔV. The control amplifier 12 has an amplifying function of proportional integration, and its output I _d ^* Is limited by the limiter 24 to the value of the current limit value f. The function unit 23 outputs a function value f as shown in FIG. 2 using the error voltage ΔV as an input deviation value, and operates using this as a current limit value. Thereby, 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 described, the current on the secondary side or the primary side of the transformer 2 may be detected.

[0022]

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

[Brief description of the 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 chart 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 chart for explaining a problem 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 controller, 16 voltage detector, 22 inverter controller, 23 function unit, 24 limiter, 25 current controller, 27 current detector, 30 proportional amplifier.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-285473 (JP, A) JP-A-3-218266 (JP, A) JP-A-2-51360 (JP, A) JP-A-62-162 210866 (JP, A) JP-A-62-217859 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M ⁷ /42-7/98 H02M 3/00-3/44

Claims (3)

(57) [Claims] Chopper means for converting a voltage of a DC power supply into a high-frequency voltage and supplying the high-frequency voltage to a primary side of a transformer;
Rectifying means for rectifying the high frequency voltage on the secondary side,
In the apparatus so as to obtain a single-phase AC voltage from the second DC voltage rectified through the rectifying means, and outputs a current reference in accordance with the voltage deviation by comparing the second DC voltage and the reference voltage and voltage control means for limiting values of the current reference is changed depending on the voltage deviation, or the voltage control unit
These current references are compared with the output current of the
Current control means for outputting a control signal in accordance with the flow deviation;
The current bias based on a control signal from the current control means.
A chop for controlling the chopper means in a direction in which the difference decreases.
DC / AC power supply, characterized by comprising a path control unit. 2. The method according to claim 1, wherein the voltage of the DC power supply is converted into a high-frequency voltage.
Chopper means for supplying to the primary side of the transformer;
Rectifying means for rectifying the high frequency voltage on the secondary side,
A single-phase alternating current from the rectified second DC voltage via the rectifying means.
An apparatus for obtaining a current voltage.
Compare the voltage with the reference voltage and set the current reference according to the voltage deviation.
And output the current reference according to the voltage deviation.
Voltage control means for which the limit value changes, and whether the voltage control means
Comparing these current references with the current on the secondary side of the transformer
Current control means for outputting a control signal according to the current deviation,
Based on the control signal from the current control means, the current
A chop for controlling the chopper means in a direction in which the deviation decreases.
DC / AC, comprising:
Power supply. 3. A method of converting a voltage of a DC power supply into a high-frequency voltage.
Chopper means for supplying to the primary side of the transformer;
Rectifying means for rectifying the high frequency voltage on the secondary side,
A single-phase alternating current from the rectified second DC voltage via the rectifying means.
An apparatus for obtaining a current voltage.
Compare the voltage with the reference voltage and set the current reference according to the voltage deviation.
And output the current reference according to the voltage deviation.
Voltage control means for which the limit value changes, and whether the voltage control means
Comparing these current references with the current on the primary side of the transformer
Current control means for outputting a control signal according to the current deviation,
Based on the control signal from the current control means, the current
Cho for controlling the pre-Symbol chopper means in the direction in which the deviation is reduced
DC / AC, comprising:
Power supply.