JPS59149746A - Resonance preventing device of power system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention detects a resonant frequency current in a received power current, detects a resonance state of a power system, and switches components of the power system to cancel the resonance. This invention relates to a prevention device.

[Technical background of the invention and its problems]

Recently, power converters using switching elements have been increasingly used at the consumer end of power systems, and as a result, harmonic currents are increasingly generated.

Furthermore, since power converters using switching elements often cause a lagging current to flow, systems in which a phase advance capacitor is inserted to compensate for the current are increasing.

In this case, the harmonic current generated by the power converter is added between the inductance on the power supply side of the main transformer and the capacitance of the phase advance capacitor, and the frequencies match and the harmonic current becomes even! Resonance may occur and harmonic currents may be abnormally amplified.

When resonance occurs, a large harmonic current flows through the main transformer, causing problems such as voltage waveform distortion and flicker.

Therefore, it is necessary for the consumer side to detect the resonance state of the power system and take countermeasures.

Conventionally, resonance detection in power systems has been performed by detecting abnormalities in the voltage level, but since the voltage level often does not change due to voltage waveform distortion or flicker, it is not possible to detect resonance based on the voltage level. It has been difficult to cancel resonance when it occurs.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a power system resonance prevention device that detects power system resonance based on a resonant frequency component in a received current and switches components of the power system to cancel the resonance.

[Summary of the Invention] The present invention provides a current detection circuit that detects a received current from a power system including harmonic components, a band elimination filter that attenuates a power frequency component of an output signal of the current detection circuit, Equipped with a level comparison circuit that detects resonance of the power system when the output level of the band elimination filter exceeds a set value, this detection signal 1: Resonance of the power system that switches the components of the power system to cancel the resonance. It is a prevention device.

Examples of the invention] An embodiment of the present invention is shown in FIG.

FIG. 1 shows the case where the present invention is applied to a stationary Servius device. In FIG. 1, grid power is applied to the primary side of a wound induction motor 2 via a main transformer 1, and the secondary power of the induction motor 2 is transferred to a rectifier 3, a DC reactor 4, a thyrisk inverter 5 and an inverter transformer. It is returned to the secondary side of the main transformer l via the transformer 6.

Since the returned secondary current is rectified by the rectifier 3, it includes the fifth, seventh, eleventh, and thirteenth harmonic currents. Therefore, a harmonic current of an order shown in the following equation +13 flows on the primary side of the induction motor 2.

l±6ns ・・・・・・・・・・・・・・・
(1) Here, 8 is slip, n is an integer of 1, 2.3, etc., and a negative number indicates that the phase rotation is reversed.

On the other hand, the combined inductance of the power supply side inductance, the leakage inductance of the main transformer l, the inductance of the phase advance capacitor series reactor 12, and the capacitance of the phase advance capacitor 14 form a parallel resonant circuit when viewed from the Serbius device side. , a specific resonant frequency ω.

have.

This resonance has a high resonance magnification Q and is narrow during resonance.

Further, since the frequency of the primary side harmonic current of the induction motor 2 changes depending on the rotation speed, the above-mentioned resonance frequency ω is reached at a specific rotation speed. may match.

The frequency of harmonic current with high content is ω. Then, the resonance is amplified and flows through the main transformer l as a large harmonic current,
This causes a large distortion in the voltage on the load side of the main transformer l and also causes flicker.

In the present invention, the current transformer 21 detects the main transformer current, the current signal detection circuit 22 converts it into a current signal, and the band elimination filter 23 eliminates the power supply fundamental frequency ω1.

That is, as the filter 23, one having a transfer function G expressed by the following equation (2) is used.

The output of the band elimination filter 23 is converted into a DC voltage level V by a level signal converting circuit 24, and compared with a level reference voltage v6 by a level comparing circuit 25. When resonance occurs and the current component at a frequency ω0 other than the fundamental frequency ω□ increases as shown in FIG. 2, it becomes v)v6, and a resonance detection signal is output.

The resonance detection signal is transmitted via the sequence circuit 31 to open and close the switching contactor 11 of the phase advance capacitor series reactor 12 and the phase advance capacitor switching contactor 13 to increase/decrease the number of them in parallel, and to adjust the resonance frequency of the system to ω. . From ω. ′ or ω. increases or decreases in the direction of I, thereby damping the resonant current.

In addition, the level comparison circuit 25 prevents its operation from being interrupted by the interlock signal 1 from the sequence circuit 31 during a transient state such as when the motor is started, thereby preventing erroneous generation of a resonance detection signal.

The sequence circuit 31 uses a microcomputer or the like to generate combinations Ll, L with different ratios of phase advance capacitor capacity and series reactor capacity, as shown in FIG.
,, Ls, etc., and when a signal indicating a resonant state is input, the resonant state is changed by changing the combination as L1 → L, -, L, → L, and changing the resonant frequency. The circuit constants of are changed to create a non-resonant state.

The operation of the sequence circuit 31 in this case is shown in the flowchart of FIG.

When resonance occurs, the output logic signal of the level comparison circuit 25 becomes constant. In FIG. 4, first, D-"O" is checked, and then if l)=wl", the combination L of the series reactor and phase advance capacitor is set to the next combination number.

Next, check whether the combination number exceeds the total number of combinations, and if it does, set L back to 1.

After that, the selected combination number is output, the sequence of this part is restored to the original, and it waits.

When a new L combination number is output, the sequence circuit 31 performs automatic power factor adjustment according to this number combination.

Since this method does not perform feedback control, hunting does not occur.

In the above explanation, it is assumed that changing the combination once will get out of the resonance state, but if the change is small and it is not possible to get out of the resonance state with one change, the next combination will be changed after a certain period of time. A similar control becomes possible by moving.

Furthermore, in the above explanation, the inductance is changed by switching the number of series reactors in parallel using a contactor, but if a saturable reactor is used as the series reactor,
Changing the excitation 1: Therefore, it is also possible to change the inductance without contact.

〔Effect of the invention〕

As explained above, according to the present invention, resonance in a power system is reliably detected by converting an abnormal rise in the harmonic component of the receiving side current into a voltage level, and By changing the combination of (1) and (1), the resonance frequency is shifted, thereby obtaining a rational power system resonance prevention device that smoothly cancels the resonance of the power system without causing hunting.

By adopting the present invention, it becomes possible to freely design a system without fear of parallel resonance even in a plant including a variable harmonic current source.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing an embodiment of the present invention, Fig. 2 is a characteristic diagram showing changes in the parallel resonance curve due to increase/decrease in the number of series reactors, and Fig. 3 is a characteristic diagram showing changes in the resonant frequency due to the combination of series reactors and phase advance capacitors. A characteristic diagram showing the changes, and FIG. 4 is a flowchart showing an example of the operation of the present invention. l Main transformer 2 Wound induction motor 3 Rectifier 4 DC reactor 5 Thyristor inverter 6 Inverter transformer 11*13 Switching contactor 12 Series reactor 14 Phase advance capacitor 22 Current signal detection circuit 23 Band elimination filter 24' Level signal conversion Circuit 25 Level comparison circuit 31 Sequence circuit

Claims (2)

[Claims] (1) A current detection circuit that detects the received current from the power system including harmonic components, a band elimination filter that attenuates the power frequency component of the output signal of the current detection circuit, and a band elimination filter that attenuates the power frequency component of the output signal of the current detection circuit. A power system resonance prevention device that rubs when the filter output level exceeds a set value. (2) A combination of a plurality of phase advance capacitors and a plurality of series reactors is used as a component of the power system, and the combination of the phase advance capacitor and series reactor is sequentially changed in accordance with the detection signal. A resonance prevention device for a power system according to claim 1.