JPH0510030B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention provides an uninterruptible power source that can switch to a bypass power supply without interruption when the frequency control section of an inverter that supplies AC power to a load fails. The present invention relates to a method of controlling an inverter for a power supply device.

[Prior art and its problems]

In order to continuously supply constant voltage, constant frequency AC power, uninterruptible power supplies that combine an inverter and a bypass power supply are often used.

FIG. 2 is a block diagram showing a conventional example of a method of controlling an inverter for an uninterruptible power supply backed up by a bypass power supply. In FIG. 2, AC power from a bypass power supply 2 is applied to a load 8 via a bypass changeover switch 3 composed of a thyristor, but normally this bypass changeover switch 3 is in an off state. Further, since a commercial power source is normally used as the bypass power source 2, the reference frequency of the bypass power source 2 is 50 or 60 Hz.

The inverter 5 converts the DC power from the DC power supply 4 into constant voltage/constant frequency AC power, and supplies this AC power to the load 8 via the transformer 6 and the inverter switch 7. The output voltage of the inverter 5 is controlled to a desired value by a voltage regulating circuit (not shown), and the frequency of the output voltage is controlled as described below.

The phase difference detector 11 detects the phase difference between the voltage phase of the bypass power supply 2 and the voltage phase of the alternating current output from the inverter 5. In other words, when the phase difference detected by this phase difference detector 11 changes from moment to moment, it means that there is a difference between the two frequencies, so the signal from this phase difference detector 11 is subjected to proportional integral calculation. The phase adjuster 12 is made to output a control signal that makes the input signal zero. The output signal of this phase adjuster 12 is converted by the frequency oscillator 13 into a signal that commands the frequency of the AC voltage outputted by the inverter 5, so that the frequency of the AC voltage outputted by the inverter 5 is changed from the bypass power supply 2. The value is equal to the frequency of the AC voltage. Therefore, when the frequency of the voltage output by the bypass power supply 2 is at the reference frequency or within a predetermined range around the reference frequency, the inverter 5 also outputs an alternating current with the same frequency, and this alternating current powers the inverter switch 7. Power is supplied to the load 8 through the power supply.

If the phase difference detector 11 or phase adjuster 12 for controlling the output frequency of the inverter 5 breaks down, the frequency of the AC voltage output by the inverter 5 cannot be maintained at the same value as that of the bypass power supply 2. Since the frequency is lost, the frequency fluctuates greatly, and the load 8 is adversely affected. Therefore, for example, the output of the phase difference detector 11 and the output of the phase adjuster 12 are inputted to the failure detector 14 to constantly monitor its status, and if an abnormality is detected, a signal is immediately sent to the failure stop circuit 17. Then, the operation of the inverter 5 is stopped by sequence control.

The synchronization detector 15 inputs the voltage of the bypass power supply 2 and the output voltage of the inverter 5 and constantly monitors whether the two are synchronized, that is, whether the voltage difference, phase difference, and frequency difference are zero. If the occurrence of the above-mentioned fault is detected and the synchronization of both is detected, the bypass changeover switch 3 is turned on by the signal from the AND element 16, and the operation is stopped before the inverter 5 is stopped by the command from the fault stop circuit 17. This inverter 5 and bypass power supply 2 are put into a parallel operation state. Therefore, if the inverter switch 7 is turned off by a command from the failure stop circuit 17, the failed inverter 5 is disconnected from the load 8, but the power to the load 8 is not interrupted.

However, if a part that adjusts the frequency of the AC voltage output by the inverter 5, such as the phase difference detector 11 or the phase adjuster 12, breaks down, the bypass power supply 2 and the inverter 5 cannot be synchronized even temporarily. Failure detector 14
Since the synchronization detector 15 does not send out a synchronization coincidence detection signal even if it outputs a failure detection signal, the inverter 5 may stop before the power supply to the load 8 is switched to the bypass power supply 2. However, there is a drawback that the power supply to the load 8 ends up being interrupted.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for controlling an inverter for an uninterruptible power supply that can reliably switch the power source to a bypass circuit without interruption even if an abnormality occurs in the frequency control system of the inverter.

[Key points of the invention]

In the present invention, when the output of the phase adjustment means is zero, the frequency of the AC voltage output by the inverter, which is operated using a bypass power supply that outputs AC of a predetermined frequency as a backup power supply, is adjusted to the frequency of the backup power supply. Since the frequencies are adjusted to be the same, when it is detected that the frequency control system of the inverter has become abnormal, a failure detection signal is given to the phase adjustment means to hold the phase adjustment means at zero, thereby inverting the inverter. will be forced to output alternating current at a frequency equal to the frequency of the backup power supply. Since the frequency of the AC voltage output by the bypass power supply at the time of this failure detection is the above-mentioned predetermined frequency or a value close to it, the AC output of the bypass power supply and the AC output of the inverter can easily be synchronized. obtain. Therefore, by connecting the bypass power supply in parallel to the inverter at the moment when it is detected that the synchronization state is reached when the above-mentioned failure is detected, and then controlling the inverter in sequence to disconnect it from the bypass power supply and stop it, This is an attempt to switch the power supply source without interruption.

[Embodiments of the invention]

FIG. 1 is a block diagram showing an embodiment of the present invention, and the details of the present invention will be described below with reference to FIG.

Since the bypass power supply designated by reference numeral 2 in FIG. 1 is generally a commercial power supply, the frequency of its output voltage is based on 50 or 60 Hz, and has a value within a very small range around this. This bypass power supply 2
AC power can be supplied to the load 8 via the bypass changeover switch 3 made up of a thyristor, but the bypass changeover switch 3 is always in an off state. On the other hand, the inverter 5 converts the DC from the DC power supply 4 into AC and outputs it.The frequency of the AC voltage output by the inverter 5 is equal to the frequency of the bypass power supply 2 mentioned above, Power is supplied to a load 8 via a transformer 6 and an inverter switch 7 which is in an on state. In this figure 1, the DC power supply 4
is a battery, but generally the DC power supply 4 is a rectified version of AC from the bypass power supply 2 or a rectified version of AC from another applicable power supply.
It is.

The inverter 5 outputs constant voltage/constant frequency alternating current, but since the constant voltage control part is unrelated to the present invention, the illustration and explanation of that part will be omitted, but the frequency of the output voltage is as follows. controlled as follows.

The phase difference detector 11 detects the phase difference between the voltage phase of the bypass power supply 2 and the voltage phase of the alternating current output from the inverter 5. This changes every moment, and when this phase difference stops changing, it means that the two frequencies have matched. Therefore, the phase adjuster 12, which is composed of a proportional-integral calculator, outputs its input signal, that is, a control signal that makes the output signal of the phase difference detector 11 zero, to the frequency oscillator 13, which is the next stage, and this frequency oscillator 13 outputs a frequency command signal to the inverter 5 such that the phase difference between the two becomes zero, that is, a command that is equal to the frequency of the AC voltage outputted by the bypass power supply 2. The frequency difference between the output voltages is zero, and the phase difference is also zero. Note that this frequency oscillator 13 is a phase adjuster 12.
When the signal input from the bypass power supply 2 is zero, a signal commanding a predetermined frequency equal to the frequency of the bypass power supply 2 is output.

By controlling the inverter 5 as described above, the bypass power supply 2 and the inverter 5 are outputting alternating current with the same frequency, but the bypass changeover switch 3 is off and the inverter switch 7 is on. , AC power from the inverter 5 is supplied to the load 8 .

If the phase difference detector 11 or phase adjuster 12 that controls the output frequency of the inverter 5 breaks down, the failure detector 1 constantly monitors the output of the phase difference detector 11 or phase adjuster 12.
4 detects this abnormality, and this failure detection signal is immediately sent to the phase adjuster 12 and the AND element 16.
given to.

Due to the fault signal given to the phase adjuster 12,
Since this phase adjuster 12 is designed to be held at zero, a zero signal is forcibly input to the frequency oscillator 13 at the next stage, and therefore the frequency of the AC voltage output from the inverter 5 is The predetermined frequency is set equal to the frequency of the bypass power supply 2 according to the frequency of the bypass power supply 2. In other words, the frequency of the AC voltage output by this inverter 5 is very close to that of the bypass power supply 2.

The synchronization detector 15 inputs the voltage of the bypass power supply 2 and the output voltage of the inverter 5, and constantly checks the synchronization state of both, that is, whether the voltage difference is zero, the phase difference is zero, and the frequency difference. Since it monitors whether or not is zero, if the two frequencies approach each other due to failure detection as described above, a synchronization matching state is detected at every cycle corresponding to the frequency difference between the two. Therefore, when the failure detector 14 is sending a failure detection signal to the AND element 16, the synchronization detector 15 detects a synchronization state between the two elements.
By sending the signal to the AND element 16,
The AND element 16 is the bypass switch 3
Since the on-command is issued at the same time, the bypass power supply 2 can be smoothly connected in parallel with the inverter 5.

At the same time, the AND element 16 is activated by the failure stop circuit 1.
Since it also sends a signal to 7, this failure stop circuit 17
The inverter switch 7 is shut off by a command from the inverter 5, and the inverter 5 is disconnected from the load 8, and further, the inverter 5 stops its operation by sequence control. In this way, even if the frequency control section of the inverter 5 fails, the power supply to the load 8 is not interrupted, and its power source is smoothly and reliably switched from the inverter 5 to the bypass power source 2.

〔Effect of the invention〕

According to this invention, even if a failure occurs in the frequency control section of the inverter and the backup bypass power supply and this inverter are out of synchronization,
By zero-holding the phase adjustment means with the fault detection signal, the frequency of the AC voltage output by the inverter is forced to the predetermined frequency (the frequency of the bypass power supply), so it operates with a slight frequency difference from the bypass power supply. It turns out. Therefore, the inverter and bypass power supply can easily become synchronized, so by connecting them in parallel and stopping the inverter the moment they become synchronized, you can prevent the power supply from failing without causing a power outage to the load. This has the effect of making it possible to smoothly and reliably switch from an inverter to a bypass power source.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional example of a method of controlling an inverter for an uninterruptible power supply backed up by a bypass power supply. 2...Bypass power supply, 3...Bypass switching switch, 4...DC power supply, 5...Inverter, 6
...Transformer, 7...Inverter switch, 8...
Load, 11... Phase difference detector, 12... Phase detector, 13... Frequency oscillator, 14... Failure detector, 15... Synchronous detector, 16... AND element,
17...Failure stop circuit.

Claims (1)

[Claims] 1. Means for detecting a phase difference between the voltage phase of a bypass power supply outputting alternating current of a predetermined frequency and the voltage phase of alternating current output by an inverter, and a control signal for reducing this phase difference to zero. and a phase adjustment means for outputting, according to the output signal of the phase adjustment means, the frequency of the voltage outputted by the inverter is made to match the frequency of the voltage outputted by the bypass power supply, so that the frequency of the voltage output from the inverter is equal to the frequency of the bypass power supply. A control method for an inverter for an uninterruptible power supply that supplies alternating current power at a frequency to a load, wherein the inverter outputs an alternating current voltage at a frequency equal to a predetermined frequency of the bypass power supply when the output signal of the phase adjustment means is zero. controlled to
When a failure of the phase difference detection means or the phase adjustment means is detected, the output of the phase adjustment means is forced to zero, and when this failure is detected, the AC output of the bypass power supply and the AC output of the inverter are synchronized. A method for controlling an inverter for an uninterruptible power supply, characterized by connecting a bypass power source in parallel to an inverter and outputting a disconnect/stop command to the inverter when a bypass power source is detected.