JPH04248316A - Overcurrent protector for power converter - Google Patents

Abstract

PURPOSE:To protect an inverter in a power converter, e.g. an uninterruptible power supply, provided with a capacitor such as a filter capacitor on the output terminal side against overcurrent which may occur for same load power factor even if the output current is lower than a rated current. CONSTITUTION:The overcurrent protector for power converter comprises a first current detecting means for detecting a current corresponding to the output current from a power converter 10, a second current detecting means 20 for detecting a current corresponding to the effective current component of output current from the power converter 10, and means 21 for producing an overcurrent protective signal when the first and second current detecting means 18, 20 have detection levels exceeding, respectively, over predetermined levels.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

[Industrial Application Field] The present invention relates to an overcurrent protection device for a power converter equipped with a capacitor such as a filter capacitor on the output terminal side, and particularly relates to an overcurrent protection device for a power converter equipped with a capacitor such as a filter capacitor on the side of an output terminal. The present invention relates to an overcurrent protection device for a power conversion device that can provide reliable protection.

0002

[Prior Art] Although there is no similar known technology related to the present invention, an example of a power conversion device is an uninterruptible power supply device. Equipment (USP) Installation Practical Guide” page
Load current waveforms and overcurrent protection are described in pages 139 to 148. With the content stated in this document, (
1) The load current waveform is as shown in Figure 5.1 or 5.2 on page 140.
As shown in the figure, it is a waveform with a high peak value that deviates from the sine waveform. (2) Load current waveform (peak value/effective value) is 1.8~
It is about 2.0.

(3) Load conditions unique to uninterruptible power supplies are shown, such as the case where a harmonic removal filter capacitor is added to the output side because the load current waveform contains harmonic current. .

FIG. 3 shows an example of the configuration of an uninterruptible power supply device known from the above-mentioned literature, in which 10 is an uninterruptible power supply device, 11 is an input AC power supply, 12 is a rectifier, 13 is a DC filter capacitor,
14 is an inverter, 15 is an output transformer, 16 is an AC filter capacitor, 17 is a load, 18 is a current detector, 19
is a protection circuit. In this configuration, the uninterruptible power supply 10 converts the AC voltage of the input AC power supply 11 into a DC voltage with the rectifier 12, smoothes this DC voltage with the DC filter capacitor 13, and converts it into a stabilized AC voltage with the inverter 14. The voltage is inversely converted and a stabilized AC voltage is supplied to the load 17 via the output transformer 15 and the AC filter capacitor 16. Further, the current detector 18 detects the output current of the uninterruptible power supply 10, and when the level of this output current exceeds a predetermined value, the protection circuit 19 performs an alarm or protective operation.

In the configuration of the uninterruptible power supply 10 shown in FIG. 3, the value of the current flowing from the inverter 14 to the output transformer 15 changes greatly depending on the phase of the output current (input power factor of the load 17).

An example of this will now be explained with reference to FIG. In FIG. 4, V1 is the output voltage of the uninterruptible power supply 10,
I11 and I12 are the output currents, Ic is the filter current flowing through the AC filter capacitor 16, I21 and I22
is the inverter output current flowing through the output transformer 15.

When the input power factor of the load 17 is poor, the output current I1 is significantly delayed in phase with respect to the output voltage V1.
1 flows. Since the inverter output current I21 flowing through the output transformer 15 becomes a current that is vectorially combined with the filter current Ic flowing through the AC filter capacitor 16, the inverter output current I21 that lags behind the output voltage V1 as shown in FIG. becomes.

On the other hand, when the input power factor of the load 17 is good,
Similarly, the output current I12 and the filter current Ic become vector-combined currents, and the inverter output current I22 at this time becomes a current whose phase leads the output voltage V1, as shown in FIG.

As is clear from the explanation of FIGS. 3 and 4,
The output currents I11 and I12 of the uninterruptible power supply 10 are the load 1
Due to the input power factor of 7, even if the input power factor is the same as shown in FIG. 4, the phase changes as described above, resulting in the inverter output current I2
It is clear that the currents 1 and I22 have greatly different absolute values and phases.

That is, in an uninterruptible power supply 10 or the like having a filter capacitor (AC filter capacitor) on the output terminal side of the power conversion device as shown in FIG. It is clear that simply providing protection with the protection circuit 19 does not provide protection appropriate to the magnitude of the current flowing inside the device.

[0011]

[Problems to be Solved by the Invention] As explained with reference to FIGS. 3 and 4 and the prior art literature, the power converter according to the prior art has the following problems.

That is, when a power conversion device has a filter capacitor on the output terminal side, such as an uninterruptible power supply, if the phase of the output current (input power factor of the load) is different, the absolute value of the output current is the same. Even in this case, the phase and magnitude (absolute value of the current) of the current flowing inside the power converter (inverter output current) will differ greatly.

Furthermore, as stated in the above-mentioned document,
The output current of the power converter is a current with a high peak value that is different from the sine wave current, so the combined current of the current close to the sine wave current flowing through the filter capacitor and the output current with a high peak value flows inside the power converter. A current flows (inverter output current), and the current flowing inside this device is also an alternating current that deviates from a sine wave. Therefore, the power conversion device according to the prior art has the following problems.

(1) When a filter capacitor is provided on the output terminal side of a power conversion device, the current flowing inside the device is not proportional to the current flowing through the output terminal, and the current flowing through the output terminal is detected. Merely performing a protective operation is insufficient to protect the power conversion device. (2) Furthermore, if a current flows whose output current has a peak value that deviates from a high sine wave, the protection described above is even less sufficient to protect the power converter.

On the other hand, if the power converter is a device with a high social responsibility, such as an uninterruptible power supply, there is a risk of causing social unrest due to the stoppage of protection of the device, so if the overcurrent factor is inside the device. It is important to determine whether the problem is caused by a load-side factor or by a load-side factor, and then provide protection.

Therefore, the present invention has been made in view of the above points, and it is possible to reliably detect overcurrent in the output current of a power converter even if a filter capacitor is provided on the output terminal side of the power converter. It is an object of the present invention to provide a highly reliable overcurrent protection device for a power conversion device. [Structure of the invention]

[0017]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an embodiment of a power conversion device 10 having a capacitor 16 such as a filter capacitor on the output terminal side, as shown in FIG. A first current detecting means such as a current detector 18 that detects a current corresponding to the output current, and a second current detecting means such as a current detector 20 that detects a current corresponding to an active current component of the output current of the power converter 10. current detection means, and protection for outputting an overcurrent protection signal under the condition that the detection level of the first current detection means exceeds a certain level and the detection level of the second current detection means also exceeds a predetermined level. circuit 21
It is characterized by having the following means.

[0018]

[Operation] With the above-described configuration, the first current detection means for detecting the current corresponding to the output current of the power conversion device detects the output current I11 in FIG. 4, for example, and detects the output current of the power conversion device. The second current detection means that detects the current corresponding to the effective current component can detect the current corresponding to the effective current component (I11COSθ11) of the current I11 in FIG. 4. Therefore, even if the output currents I11 and I12 have the same absolute value, if the power factor is θ12, the current corresponding to the effective current component (I12COSθ12) of the output current I12 will be larger.

Therefore, under the condition that the detection level of the first current detection means for detecting the output current of the power conversion device reaches a certain level, and the detection level of the second current detection means also reaches a predetermined level. Can output overcurrent protection signal.

[0020]

[Embodiment] An embodiment of the present invention is shown in FIG. In this figure, circuit components with the same symbols as in FIG. 3 are circuit components having the same functions, and 20 is a current detector;
1 is a protection circuit.

In FIG. 1, an uninterruptible power supply 10 stabilizes AC power from an input AC power source 11 and supplies it to a load 17, but the input power factor of the load 17 varies or the input current waveform is harmonic. When the output current of the uninterruptible power supply 10 contains many wave components, the output current of the uninterruptible power supply 10 is detected by the current detector 18, which is the first current detection means, and protection is provided against overcurrent exceeding the rated value of the device. A circuit 19 performs a protective operation. However, even if the output current detection signal detected by the current detector 18 does not reach the rated value of the device, if the input power factor of the load 18 is high, as is clear from FIG. There is a danger that the effective current component of the output current of the device may exceed the rated value of the device.

Therefore, the current corresponding to the active current component of the output current of the uninterruptible power supply 10 is detected by the current detector 20 which is the second current detection means, and the level of this active current detection signal is detected by the protection circuit 21. Let's do it. In order to make the present invention easier to understand, the following assumptions will be made and described in detail.

[0023] The rated output current of the uninterruptible power supply 10 is set to 10
0A The rated output power factor of the uninterruptible power supply 10 is 80%, the input power factor of the load 17 is 95%, and the load current is 95A.In this assumption, even if the output current detection signal detected by the current detector 18 is applied to the protection circuit 19, the output current Since the detection signal is less than the rated output current of 100 A, the protection circuit 19 does not detect and protect against overcurrent. However, in this assumption, the effective current component is 95A x 0.95 = 90.25A, which exceeds the rated active current component of 100A x 0.8 = 80A. Therefore, the uninterruptible power supply 10 requires some kind of protective action or alarm.

In the present invention, for example, the output current detection signal is 80
The protection circuit 19 determines that the current is equivalent to A or more, and the protection circuit 21 determines that the level of the active current detection signal detected by the current detector 20 is over 80A, so it is determined that there is an overload on the output side.
Performs protective actions, alarms, displays, etc. As described above, in the present invention, even if the output current of the uninterruptible power supply 10 is less than the rated output current, it is possible to detect at an early stage that there is an overcurrent inside the uninterruptible power supply 10 due to the load 17. Therefore, the protective operation can be performed before the uninterruptible power supply 10 fails and stops due to overcurrent.

Another embodiment of the invention is shown in FIG. In this figure, 22 is a current detector that detects the input current of the rectifier 12. Since the input current of the rectifier 12 has a predetermined relationship with the active current component of the output current detection signal detected by the current detector 18, the protection circuit 21 uses the detection signal of the current detector 22 as an active current detection signal as in FIG. protection circuit 19
Since the input current detection signal input to the protection circuit 21 is above a predetermined value and the active current detection signal input to the protection circuit 21 is at a predetermined level, it is determined that the overcurrent is caused by the load 17, and a similar protective operation is performed. be able to.

The present invention does not limit the part of the power converter at which the active current detection signal is detected, nor does it limit which level or higher the protection circuit 19 detects the output current of the power converter. It is not necessary that the current be used as long as it is close to the rated effective current determined by the rated output power factor of the power converter.

[0027] The overcurrent protection in the present invention may be an overload alarm or display of the device, or a protection stop. Various other design changes may be made without departing from the gist of the present invention.

[0028]

As explained above, according to the present invention, in a power conversion device having a filter capacitor on the output terminal side, it is possible to separate the output current of the power conversion device vectorwise into an active component and a reactive component, which is complicated and expensive. The first current detection means detects the current corresponding to the output current of the power converter, and the second current detecting means detects the current corresponding to the active current component of the output current of the power converter, without providing a detection circuit. By providing current detection means and a means for determining the detection level of these detection means and outputting an overcurrent signal, overload inside the power conversion device can be prevented even if the output current of the power conversion device is below the rated value. It is possible to provide a simple and highly reliable protection device for a power converter that can detect and protect the power converter, and further, even if the output current of the power converter is an output current with a high peak value, such as the output current of an uninterruptible power supply.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention using a single line connection.

FIG. 2 is a block diagram showing another embodiment of the present invention using a single line connection.

FIG. 3 is a block diagram showing a conventional device using a single line connection.

FIG. 4 is a current vector diagram of each part of the power conversion device for explaining the present invention.

[Explanation of symbols]

10...Uninterruptible power supply 11...
Input AC power supply 12... Rectifier 13... DC filter capacitor 14... Invar
15...Output transformer 16...AC filter capacitor 17...Load
18...Current detector 19...Protection circuit
20...Current detector 21...Protection circuit 22...Current detector

Claims (1)

[Claims] 1. An overcurrent protection device for a power converter equipped with a capacitor such as a filter capacitor on the output terminal side, comprising: first current detection means for detecting a current corresponding to an output current of the power converter; a second current detection means for detecting a current corresponding to an active current component of the output current of the power converter; and a detection level of the first current detection means exceeds a certain level, and the second current detection means 1. An overcurrent protection device for a power conversion device, comprising means for outputting an overcurrent protection signal under a condition in which a detection level of the detection level exceeds a predetermined level.