JPH01303028A - Power interruption detecting circuit for ac uninterruptible power source equipment - Google Patents

Abstract

PURPOSE:To detect interruption of a commercial power source without loss, by connecting an inverter provided with a battery with a commercial power source through a reactance thereby normally recharging the battery while feeding power from the commercial power source to a load and monitoring the battery current. CONSTITUTION:Power is fed from a commercial power source 1 through a switch 2 and a reactance 3 to a load 4 while simultaneously a battery 6 is recharged through an inverter 5. A CT is connected to point 8 between the inverter 5 and the battery 6, and the direction and the magnitude of output current therefrom are fed to an operating circuit 7. Upon interruption of the commercial power source 1, DC current flows from the battery 6 then it is reverse converted through the inverter 5 to produce AC current which is fed to the load 4 without interruption. The direction of output current from the CT inserted into point B is inverted and the inverted direction is fed to the operating circuit 7. By such arrangement, interruption of commercial power source can be detected easily and reliably without accompanying circuit loss regardless of shortcircuit or opening at the source side.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a power outage detection circuit for reliably and without loss in detecting a power outage of a commercial power source in an AC uninterruptible power supply in which a commercial power source and an inverter are connected via a reactance. It is something.

Background Art and Its Problems FIG. 2 shows a conventional example of such an AC uninterruptible power supply. In the figure, when the commercial power supply 1 is normal, the switch 2 is closed and power is supplied to the load 4 via the reactance 3. At the same time, the phase difference between the AC output voltage of the inverter 5 and the commercial power supply 1 is controlled. Storage battery 6 is charged.

At this time, if there is a power outage in the commercial power source 1, the switch 2 is opened and power continues to be supplied to the load 4 from the storage battery 6 via the inverter 5, but the problem lies in the detection of the power outage in the commercial power source 1.

When commercial power supply 1 is normal, switch 2 is closed.
If a power outage occurs in short-circuit mode (a voltage drop when the internal impedance of the power supply is small), the voltage at point A, that is, the commercial voltage, will drop, so a power outage can be easily detected by monitoring the voltage at point A. be able to.

However, if a power outage occurs in open mode (in a state where the internal impedance of the power supply is large), the inverter 5
Since the output voltage of is applied to point A through switch 2, the voltage at point A does not drop at all, and a power outage cannot be detected by monitoring the voltage at point A.

Therefore, in the past, a resistor 8 or an equivalent transformer with large loss was connected to the input of the system, and the voltage at point A,
A power outage was detected by calculating the active power at point A from the current using the calculation circuit 7 and monitoring this. That is, when the commercial power source 1 is normal, the active power is fully supplied to the inverter 5 and the load 4 from the commercial power source 1, and the active power at point A at this time is assumed to be positive. When the commercial power supply 1 is in the open mode and a power failure occurs, the supply of active power from the commercial power supply 1 to the inverter 5 and the load 4 is stopped, and conversely, active power is supplied from the inverter 5 to the resistor 8. At this time A
The active power at the point is clearly negative, and if you monitor the positive and negative values, you can detect an open mode power outage.

However, in this case, a loss due to the resistor 8 always occurs, and the active power at point A is positive.

In order to reliably discriminate negative values, the loss of the resistor 8 must be increased, and normally it is necessary to provide a loss of several percent of the device capacity. This also greatly reduced the efficiency of the device.

Means for Solving the Problems The present invention monitors active power using the current of a storage battery,
To provide a power outage detection circuit that determines whether active power is positive or negative based on the loss of an inverter, eliminates the need for a resistor, and can reliably detect a power outage without reducing efficiency unlike conventional devices. There is a particular thing.

EXAMPLES Hereinafter, the present invention will be explained with reference to the drawings. FIG. 1 is a diagram showing an embodiment of the power failure detection circuit according to the present invention. The difference from the conventional circuit is that the current of the arithmetic circuit is monitored by the current of the storage battery, and as a result, the resistor 8 is no longer necessary. That is what we are doing.

When the commercial power supply 1 is normal, the storage battery 6 is charged by the inverter 5, and the inverter 5 supplies the storage battery 6 with active power (active power minus electric power in the M flow route, so hereinafter simply referred to as electric power). Let us assume that the current at point B at this time is d.

When the storage battery 6 is fully charged, the inverter 5 stops supplying power and the current at point B becomes zero, but as long as the commercial power supply 1 is normal, the @ current will not become negative.

Here, if the commercial power supply 1 is in the open mode and a power failure occurs, power is immediately supplied from the storage battery 6 to the load 4 via the inverter 5, so the current of the storage battery 6, that is, the current at point B becomes negative. Even if there is no load 4, the current will still be negative because the inverter 5 usually has a loss of several percent of the capacity of the device.

Therefore, by determining whether the current in the storage battery 6 is positive or negative, even an open mode power outage can be reliably detected. In this case, the purpose of the resistor 8 in the conventional example is achieved by the loss of the inverter 5, so the resistor 8 is unnecessary and no loss occurs due to this.

In the figure, C and T (current transformers) are used to monitor the current of the storage battery 6, but of course a shunt resistor or the like may also be used.

Effects of the Invention As described above, according to the present invention, it is possible to reliably detect a power outage of a commercial power source without causing unnecessary loss. In addition, the calculation circuit does not require complicated AC active power calculation using a multiplier or the like, and only simple calculation of DC current is performed, so that the circuit can be greatly simplified. When we actually conducted a test using the circuit shown in Figure 1, we were able to reliably detect power outages in both short-circuit and open modes, and it was confirmed that the efficiency of the device was improved by more than a few percent compared to the conventional example.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of a power failure detection circuit according to the present invention, and Fig. 2 is a diagram showing a conventional example.
...Switch, 3...Reactance, 4...Load, 5...Inverter, 6...Storage battery, 7...Arithmetic circuit, 8...Resistance

Claims (1)

[Claims] 1. Connect a commercial power source and an inverter equipped with a storage battery using a reactance, and charge the storage battery by controlling the phase difference between the AC output voltage of the inverter and the commercial power source while constantly supplying power to the load from the commercial power source. However, in the case of a power outage in the commercial power supply, the AC uninterruptible power supply continues to supply power from the storage battery to the load via the inverter.The AC uninterruptible power supply system detects a power outage in the commercial power supply by monitoring the storage battery current. Power outage detection circuit.