JPH0250696B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an inverter in a power supply device that performs uninterrupted switching between an inverter output and another AC power source using a changeover switch, and supplies uninterruptible power to a load. It is related to the control method.

[Technical background of the invention]

Conventionally, as an uninterruptible power supply, the output of an inverter that supplies uninterrupted power by inputting storage battery power even in the event of a commercial power outage is connected to the direct commercial power supply using a changeover switch, and normally connected to the inverter via the changeover switch. When the inverter fails or when the inverter is maintained or inspected, the switch is switched to the direct commercial power supply to directly supply power to the load, and after the failure has been recovered or the maintenance inspection is completed, the switch is switched back to the inverter side and the switch is switched to the inverter side to supply power directly to the load. Devices that continuously supply power are widely used.

FIG. 1 is a block diagram showing an example of an uninterruptible power supply as described above. In the figure, 1 is a direct commercial power source, 2 is a commercial power source, 3 is a rectifier, 4 is a storage battery charged by the rectifier 3, and 5 is an inverter that receives DC power from the rectifier 3 or storage battery 4 and converts it into AC power. , 6 is an AC filter that improves the rectangular wave output of the inverter 5 to a sine wave; 7,
9 is a static type changeover switch, 8 is a load, 11 is a phase difference detector (PHD) that detects the phase difference between the direct feed commercial power supply 1 and the output of the inverter 5, and 12 is a lower frequency than the output of the phase difference detector 11. A low pass filter (LPF) that extracts only the component, 13 a voltage controlled oscillator (VCO) that oscillates at a frequency according to the output of the low pass filter 12, 14 a voltage controlled oscillator 13
A gate control circuit for the inverter 5 controls the output voltage of the inverter 5 to a constant value using the output of the inverter as a frequency reference, and 15 is a changeover switch control circuit for controlling the changeover switches 7 and 9.

The phase difference detector 11, low pass filter 12 and voltage controlled oscillator 13 are PLL (Phase Locked
Locp) circuit is configured to control the frequency of the inverter 5 so that the output phase of the inverter 5 matches the phase of the direct commercial power supply 1. At all times, selector switch 7
is ON, the changeover switch 9 is OFF, and the inverter 5 supplies power to the load 8. On the other hand, if the inverter 5 breaks down for some reason, the changeover switch 9 is immediately turned on and the changeover switch 7 is turned off, so that the load 8 is directly supplied with power from the direct commercial power supply 1 without momentary interruption. Further, when performing maintenance and inspection on the inverter 5, by manually switching from the changeover switch 7 to the changeover switch 9, power is directly supplied from the direct commercial power supply 1 in the same manner as described above. Subsequently, when the inverter 5 recovers from a fault or the maintenance inspection is completed, the changeover switch 9 is switched again to the changeover switch 7, and the direct commercial power supply 1 is returned to the inverter 5 to supply power to the load 8 without momentary interruption. do.

[Problems with background technology]

However, when the direct commercial power supply 1 is returned to the inverter 5, the load on the inverter 5 changes suddenly from no load to full load, so the output voltage fluctuates greatly during the switching transition, which adversely affects the load 8. Furthermore, even if a sufficient wrap period is provided between the changeover switch 9 and the changeover switch 7 when switching from the changeover switch 9 to the changeover switch 7, the impedance of the AC filter 6 connected to the output of the inverter 5 is Since the impedance of the inverter 5 is considerably large compared to the impedance of the switch 7 and 9, the direct feed commercial power supply 1 will share most of the load current to the load 8 during the wrap period of the switch 7 and 9, and the output of the inverter 5 will not be output until the switch 9 is turned off. Since the current increases, an output voltage fluctuation occurs that is almost the same as the sudden load change from no load to full load described above.

To reduce this voltage fluctuation, there are methods to install an inverter with a larger capacity than necessary, or to install a PWM inverter with complicated control as an inverter with low internal impedance, but there are problems in terms of economy. There is.

[Purpose of the invention]

The object of the present invention was to provide a frequency control circuit that connects the output end of an inverter and another AC power source using a changeover switch and controls the output phase of the inverter to match the phase of the AC power source. An object of the present invention is to provide an inverter control method that does not cause fluctuations in output voltage when switching from an AC power source to an inverter using the changeover switch.

[Summary of the invention]

To achieve this objective, the present invention suppresses fluctuations in output voltage by controlling the inverter's output phase so that it gradually increases during switching until the inverter's output current matches the load current. be.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described with reference to FIG. In Fig. 2, the same reference numerals as in Fig. 1 represent the same parts as in Fig. 1, so the explanation thereof will be omitted. CT.21 detects the inverter output current. CT.22 detects the load current. CT.23
is a changeover switch control circuit, and 24 is a command from the changeover switch control circuit 23 to control CT.22 and CT.23.
25 is an analog adder that provides the deviation between the output of the phase difference detector 11 and the output of the proportional integrator to the low-pass filter 12. . The polarities of the proportional integrator 24 and the analog adder 25 are selected so that they operate in the direction of advancing the inverter output phase so that (inverter output current)<(load current).

A specific example of the proportional integrator 24 is shown in FIG. 31 is an operational amplifier, 32 is an analog switch (normally ON, turned OFF by an integration start command) 3
3, 34, and 35 are resistors, and 36 is a capacitor.

Next, the operation of the embodiment shown in FIG. 2 will be explained. FIG. 4 is a time chart for explaining the operation of each part of the embodiment shown in FIG. Changeover switch 7 is OFF,
When switch 9 is ON, proportional integrator 2
The output of inverter 4 is zero, and the output phase of inverter 5 is controlled to match the phase of direct commercial power supply 1.
Next, when the changeover switch 7 of the inverter 5 is turned on at time _t1 , at the same time, the changeover switch control circuit 23 gives an integration start command to the proportional integrator 24, and the proportional integrator 24 connects to the inverter output power source as shown in FIG. Integration of the deviation from the load current is started, and the output of the proportional integrator 24 is applied to the low-pass filter 12 through the analog adder 25. As the output of the proportional integrator 24 interrupts the PLL circuit that controls the output phase of the inverter 5 in this manner, the output phase of the inverter 5 shifts in the leading direction. It is well known that in a parallel system of AC power supplies, load sharing is determined by the phase of each power supply, and during the wrap period of the changeover switches 7 and 9 (from t ₁ to t in FIG.
_t2 ), as the output of the proportional integrator 24 gradually increases and the output phase of the inverter 5 gradually shifts to the advancing direction, the load also gradually shifts from the direct commercial power supply 1 to the inverter 5, as shown in FIG. The output power of the inverter 5 gradually increases as shown in FIG. Since the output voltage control system of the inverter 5 responds at a speed sufficiently faster than the slope of the increase in output current, almost no fluctuation in the output voltage occurs. Note that the output of the proportional integrator 24 becomes balanced when the deviation between the load current and the inverter output current becomes zero and becomes a constant level, and the output phase of the inverter 5 also becomes constant at θ _H. In other words, a kind of constant current control loop is formed based on the load current.

At the time _t2 when the load transfer from the direct commercial power supply 1 to the inverter 5 is completed, the changeover switch 9 is turned off, the integration command to the proportional integrator 24 is released, and the output of the proportional integrator 24 is reset to zero. , the PLL circuit operates so that the output phase of the inverter 5 matches the phase of the direct commercial power supply 1, and the state shifts to a state where the regular inverter 5 supplies power to the load.

Furthermore, since the slope at which the inverter output phase gradually advances and the final value θ _H are based on the load current, they are optimally controlled according to the load current so that no cross current occurs between the direct feed current 1 and the inverter 5.

In the embodiment shown in FIG. 2, a case has been described in which a commercial power source is used as the other AC power source, but similar effects can be obtained by using various power sources as the other AC power source. For example, the other AC power source may be a commercial power source via an automatic voltage regulator (AVR), a private generator, or an inverter.

[Effects of the Invention] As explained above, according to the present invention, voltage fluctuation occurs when switching from the AC power source to the inverter in a power supply device in which the output end of an inverter and another AC power source are connected by a changeover switch. No high quality power supply can be constructed.

Furthermore, it is advantageous in terms of economy because it is only necessary to add a simple configuration of a current transformer and a proportional integrator.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional uninterruptible power supply, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 is a specific example of the configuration of the proportional integrator in FIG. The circuit diagram and FIG. 4 are time charts explaining the operation of each part of the embodiment shown in FIG. 1... Direct commercial power supply, 2... Commercial power supply for inverter, 3... Rectifier, 4... Storage battery, 5... Inverter, 6... AC filter, 7, 9... Changeover switch, 8... Load, 11 ...Phase difference detector (PHD), 12 ...Low pass filter (LPF), 1
3... Voltage controlled oscillator (VCO), 14... Gate control circuit, 15, 23... Changeover switch control circuit, 21, 22... CT, 24... Proportional integrator,
25...analog adder, 31...operational amplifier,
32...Analog switch, 33, 34, 35...
...Resistor, 36...Capacitor.

Claims (1)

[Claims] 1. In a power supply device in which the output end of an inverter and another AC power source are connected by a changeover switch, when the changeover switch switches the load from the AC power supply to the inverter without interruption, the load current and the output current of the inverter are An inverter control method, characterized in that the output phase of the inverter is controlled so that the output current of the inverter matches the load current using an output obtained by proportionally integrating the deviation between the inverter and the load current.