KR910008549B1 - A.c. power supply - Google Patents

Abstract

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Description

AC power supply

1 is a block diagram showing a basic configuration of an AC power supply apparatus according to an embodiment of the present invention.

2-5 are block diagrams showing conventional systems.

6 is a main circuit diagram of one embodiment of the present invention.

7 is a circuit diagram showing an example of a switch used in the cycloconverter portion of the present invention.

8 is a waveform diagram for explaining the operation of the cycloconverter of the present invention.

9 and 10 show the structure of another embodiment of the present invention.

11 is a circuit diagram showing another embodiment of converting a commercial power source into a high frequency wave.

12 is a block diagram showing an example of a control circuit of the present invention.

(The same reference numerals in the drawings indicate the same or equivalent parts.)

* Explanation of symbols for main parts of the drawings

1: inverter 3: charger

5: commercial power supply 6: converter

The present invention relates to an AC power supply such as an uninterruptible power supply (hereinafter abbreviated as UPS) or a fuel cell power generation system of the present invention.

The configuration of a typical representative UPS is shown in FIG. In the figure, the charger 3 converts the power of the commercial power supply 5 into direct current, and supplies the direct current power to the voltage inverter while charging the battery 2.

The inverter 1 converts the DC power into AC power of low order harmonics, and then converts the DC power into AC power of a sine wave through a filter composed of a reactor Ls and a capacitor Cp, and a transformer. and by (T _2), converted to a voltage for the load is supplied to the load (4).

In general, a load of a UPS, such as a computer, is often insulated from the power supply side to prevent noise, and then a dedicated ground is provided. The transformer T ₂ is required not only for the voltage but also for the function of insulation.

The transformer T _{1 on the} power supply side is often omitted, but since the voltage on the DC side of the inverter is often determined by the economics of the inverter and the battery, the transformer T ₁ is often transformed and insulated at the voltage.

In the conventional UPS of the most conventional design, since two transformers are required, its weight and dimensions are large, making it difficult to miniaturize and reduce the size of the UPS. A new scheme devised to solve this problem is the high frequency intermediate link scheme shown in FIG.

FIG. 3 shows a UPS having the same function as FIG. 2 based on the DC / AC converter by the high frequency intermediate link shown in FIG. 14 of the article "About the Classification of the Inverter and Its Characteristics" in the November, 1981 issue of P987-992. It is made up.

In the figure, the inverter 1 is a voltage inverter for generating a single-phase square wave of, for example, f ₁ = 10 KHZ, and its output is insulated from the transformer T ₂ and then applied to the cycloconverter 6.

The cycloconverter 6 converts the power of the frequency f ₁ into power of, for example, f ₂ = 60 Hz, and converts the sine wave through a filter composed of the reactor Ls and the condenser Cp to supply the load.

In this method, the transformer T ₂ can be designed at a frequency of 10 KHZ, which can be extremely small and light in weight. However, the part of the charger requires a transformer T ₁ of commercial power frequency f _{2 as} shown in FIG.

To improve this, the system that has been re-developed is shown in FIG. This is the same high frequency intermediate link method applied to the charger, noting that the DC / AC converter of FIG. 3 can be reversibly operated.

However, this method can reduce the size of the transformer, but the efficiency is lowered and the price of the converter becomes expensive because it passes two cycloconverters and two inverters between commercial inputs and outputs.

Therefore, the method of FIG. 4 is possible in principle, but has little practical value in terms of economic efficiency and efficiency. To remedy this shortcoming, a new design was devised from the INTELEC '87 Conference Proceeding. Section 12. P516 to 520 is an unnecessary method for the charger as shown in Fig. 16 (b) of “Small UPS using phase control”.

This method is shown in FIG. 5 in accordance with the drawing method of FIGS. 2 to 4 of the present invention.

In this system, when the commercial power supply 5 is normal, it is supplied to the load 4 as it is through the switch SW, and at the same time, the cycloconverter 6 is converted into the power of f ₁ and the inverter 1 is converted into direct current power. It converts and charges the battery (2).

When the commercial power supply is out of power, the switch SW is opened, and the battery power is supplied to the load 4 through the inverter 1 and the cycloconverter 6.

This method is very practical because it requires only two converters, but it is not applicable to the applications requiring exact constant frequency because the power supplied to the load becomes the same voltage and frequency as the commercial power supply.

The present invention solves the need for a large number of converters between the commercial input to the AC output, which is a drawback of the conventional high frequency intermediate link UPS such as FIG. 3 and FIG. To provide a means.

The present invention provides a converter which is required by having a star configuration such that all three of energy from a commercial power source, energy from a battery, and energy to a load are traded across a power of a common frequency (F ₁ ). It is a small number.

As the configuration and by the power from the commercial power supply to the first converter converts a frequency of the high frequency (f ₁₎ and supplied to the bus (B _1).

There is a second reversible converter between the AC bus B ₁ and the battery 2, and the battery is charged by AC / DC conversion of the AC bus B ₁ , or when the commercial power supply is out of power. DC / AC conversion of power is supplied to AC bus B ₁ .

The third converter uses a cycloconverter or the like to convert the power of the bus B ₁ into the power of the frequency f ₂ and supply it to the load 4.

In this configuration, when there is a commercial power source, power is supplied to the load through two converters, a first converter and a second converter.

In addition, the charging power only passes through two of the first converter and the second converter. In the case of power failure, the power of the battery is converted into an alternating current of frequency f ₁ by the second converter and then supplied to the load through the third converter.

As described above, in the present invention, the power always passes through two converters, and a high efficiency system can be provided.

EXAMPLE

Based on FIG. 1, which is a block diagram of the present invention, a specific embodiment is shown in FIG.

In FIG. 6, the inverter 10 is a square wave inverter made up of transistors Q _{1 to} Q ₄ and diodes D _{1 to} D ₄ , in which voltage control is not performed and corresponding to the voltage of the battery 2. The square wave is supplied to the bus bar B ₁ .

The inverter 10 fixes the frequency and establishes the voltage and frequency of the bus B ₁ by the inverter 10 as a reference for the whole system.

The converter 11, which consists of a diode rectifier 11-B, a transistor inverter 11-A, and a capacitor C ₀ , converts the power of the commercial power supply 5 at the same frequency f ₀ as that of the inverter 10. Convert to power.

At this time, the inverter 11-A controls the PWM control of the output voltage and the phase advance with respect to the voltage of the bus B ₁ of the generated voltage and sends the power to the bus B ₁ to control the power. The power for charging the battery 2 through 10 and the power supplied to the load through the cycloconverter 12 are adjusted.

Reactor L _A has an impedance of about several percent to 30% PU, but this is a high water flowing due to the difference between the uncontrolled short wave of bus B ₁ and the PWM waveform of inverter 11-A. I) is suppressed, and the inverter 11-A is fed into the bus B ₁ to facilitate the control of the amount of power.

Since the voltage of the bus B ₁ is fixed to a nearly perfect square wave by the battery 2 and the DC flat capacitor C _{a in} parallel therewith, the cycloconverter 12 mutually influences independently of the inverter 11-A. It works without receiving.

If the number of f ₁ is KHz or more and f ₃ is 60 Hz, the cycloconverter 12 is applied only to the natural current type or the self extinguishing type.

In this case, the switches S _{1 to} S ₆ may be formed of a self-extinguishing type switch as shown in Figs. 7A and 7B.

In the embodiment of FIG. 6, the operation of the cycloconverter will be described in detail.

If the inductance of the transformer T _{2 of} FIG. 6 is sufficiently small, a square wave similar to the bus B ₁ as shown in FIG. 8 (a) is obtained on the secondary side.

The capacitor C _A is a surge absorber installed to facilitate the switching of the cycloconverter. First, when V _RS is positive as in the first half cycle of FIG. 8, when the switch S ₁ is turned ON, a positive voltage at the X point turns on the switch S ₂ . When turned ON, a negative voltage is obtained at the X point.

In addition, when V _Rs is negative, the same voltage is obtained at the X point when S ₁ and S ₂ are controlled.

Turning on S ₁ and S ₂ at the same time should shorten the secondary side of the transistor. Turning off both switches (S ₁ ) and (S ₂ ) at the same time should be avoided since the current path of the reactor (L _SU ) is lost.

In FIG. 8, a sawtooth wave is generated as shown in the diagram (b) in a half cycle of the transformer (T ₂ ) secondary voltage (V _RS ) of the drawing (a), and the intersection of the control signal represented by the wire of the drawing (b). The timing of switching between the switches S ₁ and S ₂ is determined by the point.

8D shows that the voltage with respect to the virtual center point of the X point gradually increases as the control signal increases. (Furthermore, as the virtual center point, think about the midpoint of the secondary winding of the transformer T _2. )

As can be seen from this figure, the switching of the switch is determined by the magnitude of the sawtooth wave and the control signal and the polarity of the voltage V _Rs .

Now, if R is the positive half-cycle for S, then T = 1 / (2f ₁ ), but the first half of this period (T _A ) is the switch (S ₁ ) turned on, the second half T _B = T-T _A When the switch S ₂ is on, the average voltage of this period T with respect to the virtual center point N of the voltage at the X point becomes as follows.

V _x = V _s (2T _A / T-1)

However, V _S is the voltage between RS.

From this, it can be seen that the average voltage at the X point can be converted in the range of -V _s to V _s by controlling T _A.

Although the above description only describes the U phase of the cycloconverter of FIG. 6, the converter with the same sawtooth wave is installed on the V and W phases, respectively, to output to these three converters so as to control the switches S ₃ and S ₄ . By giving a control signal corresponding to the three-phase voltage, the voltage at the X, Y, and Z points is converted into a three-phase sine wave, so after passing through the filter, the three-phase sine wave can be obtained at the output terminals U, V, and W. .

In the embodiment of FIG. 6, two transformers T ₁ and T ₂ are used, but this can be concentrated in one transformer as shown in FIG.

In this figure, the converter having the same function as that of FIG. 6 is omitted and is indicated by a block. In this figure, the transformer has three windings and most of the output of the transformer 11 is supplied to the cycloconverter 12 via the winding W ₁ to W ₂ .

In addition, part of this output is AC / DC converted as the reverse operation of the inverter 10 via the winding W ₃ to charge the battery 2.

In the case of power failure, the inverter 10 converts the power of the battery into DC / AC, and the windings W ₃ and W ₂ are totally supplied to the cycloconverter 12.

Thus, in the method of FIG. 9, power is always passed through only one transformer, so the efficiency and economy are excellent.

It is also possible to omit the winding W ₃ in FIG. 9 and to connect the output of the inverter 10 to the winding W ₁ or W ₂ .

In the above description, the case where the inverter 10 is always operated is described, but the inverter 10 may be operated only during a power failure.

At this time, in order to stabilize the voltage of the bus B ₁ when the inverter 10 is operating in FIG. 6, the capacitor C _A is enlarged to 40 to 100% PU so that the voltage of the bus B ₁ is increased. Stabilize the voltage in sinusoidal phase.

Moreover, in order to respond to the voltage difference between the sine wave of the bus B ₁ and the square wave of the inverter 10, a reactor of 20 to 30% PU may be provided in series at the output of the inverter 10. The cycloconverter 12 performs phase control on the basis of the changing single-phase sine wave of the bus B ₁ to generate a three-phase sine wave well.

In this embodiment, the battery 2 can be charged. That is, by the PWM control of the inverter 11-A, the power is rectified by the diodes D _{1 to} D ₄ of the inverter 10 in which the voltage of the bus B ₁ is changed to charge the battery 2. (In this case transistors Q ₁ to Q ₄ are on without switching)

In case of power failure, the inverter 10 is immediately started to secure the bus voltage. In this case, even if the battery voltage is changed by the PWM control of the inverter 10, the bus voltage of B ₁ can be kept constant.

In the above embodiment, the inverter 10 has been described in the case of using a single-phase inverter, but it is known that the cycloconverter 12 can operate even in a three-phase sine wave power source.

Therefore, the inverter 10 of FIG. 9 can be used as a three-phase sine wave inverter as shown in FIG.

In FIG. 10, the inverters 10-A, 10-B, and 10-C are single-phase bridge inverters, respectively. Control to keep the voltage of C _A ) constant. The converter 11 controls the power injected into the winding W ₁ through the reactor L _A by controlling the advancing of the output voltage with respect to the voltage of the capacitor C _A.

The cycloconverter 12 supplies stable 8-phase 60 Hz power to the output terminals U, V, and W based on the stable high frequency three-phase voltage established in the capacitor C _A. The eight-phase intermediate link is suitable for large power supplies because it can obtain good output waveforms at relatively low intermediate link frequencies.

In the description of the discrete FIG. 6, a combination of a rectifier and an inverter is applied to the converter 11. Instead, an eight-phase / two-phase cycloconverter as shown in FIG. 11 may be used.

Further, in FIG. 11, the switches S ₁ to S ₆ may use a switch as shown in FIG.

Next, an embodiment of a control circuit for embodying the present invention will be described with reference to FIG.

In this example, the bus B ₁ is a single-phase sine wave of high frequency f ₁ , and the bus voltage is controlled as a constant voltage constant frequency in the inverter 10, and then the cycloconverter 12 and the inverter 11 are controlled based on the reference voltage. That's the way it is. Transformers are omitted for simplicity.

The inverter 10 has a single-phase bridge configuration and controls the voltage of the bus B ₁ by PWM control of one pulse. The frequency of this inverter is fixed as an oscillator (OSC), and the voltage reference (V _B ^* ) is based on the feedback signal from the voltage sensor (VS ₂ ), and the voltage control (VC ₂ ) controls the output pulse width of PWM ₂ . To control the bus voltage (V _B ) to a constant value.

The cycloconverter 12 phase-controls the sinusoidal single-phase power of the bus B ₁ to obtain sinusoidal power of single-phase 60 Hz at the output. If the frequency of bus (B ₁ ) is high enough for the output 60Hz, such as 600Hz or more, the filter of relatively small reactor (Ls) and condenser (Cp) removes harmonics sufficiently and generally the distortion rate ( I) Sine waves of 8 to 5% or less can be obtained.

The control circuit of this cycloconverter is provided with a current minor loop for controlling the instantaneous value of the output current.

The no-load voltage is established by giving Ic ^* = Icmcosωt = ωCpVcmcosωt as the current reference to flow to the output filter capacitor Cp in this current minor loop.

The load current I _L is then fed forward to quickly follow the load change and operate as a low voltage source of impedance.

Finally, Vc ^* = Vcmsinωt is made in the sinusoidal voltage command generation circuit REF, and the control signal of the voltage controller VC ₃ is added to zero the difference between the voltage command and the actual voltage.

The sum of the eight signals is limited to within the allowable current value of the cycloconverter in the limiter LIM, and is given as a command value of the current minor loop. In this way, the cycloconverter 12 can obtain a sinusoidal wave single phase of 60 Hz by the single-phase high frequency power supply established in the bus B ₁ .

Next, the control of the inverter 11 which supplies the required power of this system will be described. The frequency and phase of the inverter are determined by the voltage controlled oscillator (VCO).

The center frequency of the VCO is set as f ₀ = mf ₁ and dropped to the frequency of f ₁ as the counter CNT ₁ of the m counter and applied to the modulation circuit PWM ₁ .

This PWM circuit applies a signal of one pulse PWM to the inverter 11 and controls the output voltage of the inverter 11. Voltage control is to control the average value of the voltage V ₁ in front of the reactor LA to the command value V ₁ *. The signal is based on the average value obtained by the voltage controller VC ₁ as the voltage sensor VS ₁ . V ₁ ^* -Controls V ₁ to be 0.

The center phase of the generated voltage V ₁ of the inverter 11 is obtained at CNT ₁ , and the advance angle ΔØ to the voltage V _B of the bus B ₁ is obtained as the phase detection circuit PD.

This ΔØ is controlled by the PLL amplifier A ₁ in response to the required power of the system. Since most of the power required in the system is input to the cyclo converter 12, the power P ₁ is obtained as a multiplier MIT, smoothed as a filter FIL, and then a phase difference command corresponding to this power ( ΔØ ₁ ^* ) to the PLL amplifier.

Next, in order to charge the battery 2, the amplifier A ₂ is operated so that the difference between the voltage command V _D ^* and the present value V _D is zero, and the phase signal corresponding to the charging power ΔØ ₂ ^* ) Is given to the PLL amplifier A ₁ .

Again, the phase difference signal ΔØ ₃ ^* corresponding to the no-load loss of the inverter 10 is applied to the PLL as a bias.

In this way, the PLL amplifier A ₁ adjusts the frequency of the oscillator VCO very little so that the INV ₁ can supply the power required by the system to the bus B ₁ .

By connecting nine converters to a common high frequency bus bar in the form of a star, an AC power supply device using a high frequency link type conversion system can be configured with fewer converters than the conventional method.

As a result, the number of converters to pass along with the power conversion is reduced and the efficiency is improved. When this device is applied to uninterruptible power supply systems, it is possible to obtain a compact, lightweight and highly efficient system.

Claims (3)

A first converter converting an AC power source having a second frequency into a first frequency higher than the second frequency, and a reversible power source converting the DC power source into an AC power of the first frequency. And a third converter convertible from at least one of said first and second converters to convert to a third frequency and supply it to the load. The transformer of claim 1, wherein a transformer having three sets of windings is installed, the output of the first converter is connected to the first winding, the output of the second converter is connected to the second winding, and the input of the third converter is removed. AC power supply, characterized in that connected to three windings. The battery according to claim 1 or 2, wherein the DC power is used as a battery, the second converter is a voltage inverter, and the output of the first converter is rectified as a feedback diode of the voltage inverter to charge the battery. AC power supply, characterized in that.

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