JPH0322828A - Harmonic compensation/control method for phase advance capacitor - Google Patents

Abstract

PURPOSE:To eliminate extension of capacitors by connecting a static power converter comprising a high frequency switching element to the source side of a phase advance capacitor and connecting a CT to the source side then injecting current for cancelling the harmonics. CONSTITUTION:Upon occurrence of harmonics in the system, reactive current Iq+Ih containing higher harmonic component Ih (Iq is sinusoidal reactive current) flows into a phase advance capacitor Ca. Harmonics contained in Iq and having a plurality of frequencies are fed, together with Iq, to the operating section 31 in a controller 3 forming a harmonic compensator 1 through a CT1, where only Ih is extracted and operation of -Ih having reverse polarity is carried out. Output current of a static power converter 2 is fed back from a feedback signal CT2 and added to -Ih, then PI control is performed through a regulator 32. The harmonic current -Ih outputted from the power converter 2 is injected through a transformer T2 and a circuit breaker Bi into the power capacitor Ca, where it is cancelled by +Ih, and only Iq is injected to the capacitor Ca. By such arrangement extension of capacitor is not required even if higher harmonics increase due to modification of load.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a phase advance capacitor connected to a power transmission and distribution system to prevent abnormal phenomena such as abnormal noise or heating/burning caused by the inflow of harmonics into a phase advance capacitor. Concerning harmonic compensation control method for capacitors. (Prior art) A phase advance capacitor is used by being connected to the load side of a branch point in order to absorb the reactive current of the system. For example, in the power distribution system diagram of FIG. 2, power is distributed from the upper power feeding system to the lower power feeding system via the power receiving transformer T1. The lower feeding system further includes each load device L1.
~ Ln is configured so that the power is branched and distributed. Also,
A phase advancing capacitor C1S is connected to the lower feeding system in the figure to absorb reactive power. In addition, the figure B a
, Bh~Bn, Bc indicate circuit breakers. (Problem to be solved by the invention) By the way, harmonics may occur in the power distribution system. In particular, today, when semiconductor power conversion devices such as inverters that tend to generate harmonics are becoming widespread, the generation of excessive harmonics has become noticeable due to the addition or modification of such devices. Such harmonics distort the sine wave flowing through the system, and as a result, a sine wave reactive current with a distorted waveform flows through the phase advancing capacitor Ca. Therefore, if measures against harmonics are not taken, the capacitor Ca will generate abnormal noise or be heated beyond its rating, and in the worst case, the phase advance capacitor Cl1 will burn out. ．． Conventionally, in order to prevent such a situation from occurring, measures have been taken such as installing new harmonic filters in each of the load devices L1 to Ln or placing restrictions on their operation. Although this suppresses the harmonic duty of the phase advance capacitor Ca, it is inconvenient that installing a new filter etc. is troublesome for the consumer and also increases the economic burden. Further, depending on the case, the capacitor capacity may be increased by replacing or reinforcing the phase advance capacitor Ca to prevent the above-mentioned situation. In this case, as the harmonics increase. In each case, it is necessary to replace the phase advance capacitor Ca. In addition, it is necessary to perform the above operations promptly to maintain the reliability of the system. Therefore, there are disadvantages in that the economic and time burden required for this work increases, and the phase advance capacitor CI1 lacks versatility.
There was also the problem of hindering the smooth operation of the entire system. Furthermore, even if harmonics occur or increase in the upper feeding system, these harmonics will flow into the lower feeding system, so There is a risk of burnout of the phase advancing capacitor CI1, and
Inconveniences and problems will arise due to the replacement of I. The present invention has been made in order to solve the above problems, and eliminates harmonic components contained in the reactive current flowing into the phase advancing capacitor, thereby making it possible to connect the system to the load equipment without the need to attach a filter to the load equipment. The purpose of this paper is to provide a highly versatile harmonic compensation control method for phase advance capacitors that ensures smooth overall operation. (Means for Solving the Problems) In order to achieve the above object, the present invention first constructs a harmonic compensator using a static power converter including a high frequency switching element and a control device, and The output terminal of the static power converter is connected to the power supply side of the phase advancing capacitor provided inside. And the control device is
A harmonic component contained in the reactive current flowing into the phase advance capacitor via a current detector provided on the power supply side from the point where the output terminal is connected is extracted and calculated, and then the calculation result is calculated. Based on this, a harmonic current that cancels the harmonic current is injected from the static power converter into the phase advancing capacitor. (Operation) When harmonic components are superimposed on the healthy sine wave current flowing through the system, distortion occurs in the sine waveform. In other words, harmonic components are apparently missing from the sine waveform.
Normally, the reactive component of the sine waveform with some of the harmonics missing would flow through the phase advance capacitor, causing the capacitor to burn out. In contrast, in the present invention, first, a harmonic compensator is constructed to remove the harmonic components included in the reactive current flowing into the capacitor, in other words, the harmonics missing from the sinusoidal reactive current at the waveform hill. Extracted and calculated by a certain control device. Then, the control device controls the static power converter based on this calculation result. That is, the static power converter is controlled so as to output a harmonic current that compensates for some harmonics missing from the reactive sine wave current flowing into the phase advancing capacitor.

Here, it is preferable that the harmonic compensator has a current feedback system. Furthermore, high-frequency switching devices such as power transistors and GTOs are used as switching elements constituting static power converters. As a result, a high-frequency current with a polarity opposite to some of the harmonics contained in the reactive current is generated with high precision and injected into the phase advance capacitor, achieving high-speed response characteristics. As a result, reactive current containing harmonic components from the system or upper system, and harmonics of opposite polarity to the harmonics from the static power converter flow into the phase advancing capacitor.
Harmonic components are canceled out. As a result, the inflow of reactive current with missing harmonics of the phase advance capacitor 8 is apparently eliminated, and only the reactive component of a pure sine wave flows. Able to accomplish his responsibilities without obstacles. (Example) Hereinafter, an example of the present invention will be explained with reference to FIG. In the same figure. Tz, L1-Ln. Ca. B++, Bt~Bn
, Bc are the same as the elements denoted by the same reference numerals in FIG. 2, and detailed description thereof will be omitted. In this embodiment, the phase advancing capacitor C. This harmonic compensator 1 is connected to a terminal power distribution system including a static power converter 2 and a control device! 3. In this embodiment, the static power converter 2 is composed of high-frequency transistors, and
The control device 3 includes a calculation section 31. @Arbitrator 32 and adder 33
It is composed of etc. And static power converter 2
The output terminal of is connected to the power supply side of the phase advance capacitor Ca (connection point P), and a harmonic detection transformer CT1 is provided at a point further above this connection point P (power supply side). ．． This detection transformer CT. The signal from is input to the control unit [3]. Further, on the output side of the static power converter 2, a transformer Ts
A feedback signal transformer CTz is provided via the feedback signal transformer CTz, and the signal from the feedback signal transformer CTi is fed back into the control unit W13.

Note that FIG. 1 shows the system using a single line connection diagram, and although the components for each component are not shown for three phases, control is actually performed for the three phases.

Next, we will explain this operation. Now, if harmonics occur in the grid, the reactive current Iq + Ih containing the harmonic component Ih
(Iq is a sine wave reactive current) flows into the phase advancing capacitor Ca. here. Ih has multiple frequencies. Then, the harmonic detection transformer CT. The calculation unit 31 in the control device N3 extracts the harmonic component Ih contained in the inflow current, and calculates the waveform Ih of the opposite polarity of the harmonic. In other words, the calculation unit 31 is a pure Calculate the harmonic component -1h that appears to be missing on the waveform from the sine wave reactive current I9. Then, this calculation result is sent to the adjuster 32 via the adder 33.
is output to. The adder 33 includes a feedback signal transformer CT3.
The actual value of the output current of the static power converter 2 is fed back from the controller 32, and the regulator 32 performs well-known operations such as PI control. And static power converter Ii! 2 outputs harmonic current -Ih, and this harmonic current -1h is connected to transformer Tx.
．． It is injected into the phase advancing capacitor C● via the circuit breaker Bi. This happened. The impedance of the load devices L1 to Ln seen from the static power converter 2 is high, and the impedance of the advancing capacitor CI1 is low, so the harmonic -1h flows only into the advancing capacitor CII. Then, the harmonic components Ih and -Ih originally included in the reactive current flowing in from the grid side cancel each other out. As a result, only the pure sinusoidal reactive current 9 flows through the phase advance capacitor Ca, so that the phase advance capacitor CII can fulfill its duty without requiring an increase in its capacity.

In the above embodiment, the static power converter 2 is provided at the lowest branch point in the lower feeding system, and the phase advancing capacitor Ca is connected to the immediately higher branch point. The invention is based on the phase advancing capacitor Ca, the static power converter 2, and the harmonic detection transformer C T 1 shown in FIG.
For example, in FIG. 1, the static power converter e12 is connected to the power supply side of the phase advancing capacitor CII, and the harmonic detection transformer C T is further connected to the power supply side. z may be connected to compensate for harmonics.

Furthermore, although the above embodiment describes a harmonic compensation control method for a phase advance capacitor provided in a power distribution system, the present invention is also applicable to a phase advance capacitor in a power transmission system. (Effects of the Invention) As described above, according to the present invention, harmonic current having a polarity opposite to the harmonics included in the reactive current flowing into the phase advance capacitor can be injected into the capacitor by the compensation control device. Therefore, even if the harmonics of the line increase due to the addition or change of loads connected to the system, the waveform of the reactive current flowing into the phase advancing capacitor becomes a sine wave. Therefore, it is possible to prevent abnormal noise, abnormal heating, and burnout of the phase advancing capacitor installed in the load equipment. In addition, the burden on consumers such as installing new harmonic filters on load equipment and restricting the operation of load equipment is reduced, and there is no need to increase capacitor capacity by replacing or reinforcing phase advance capacitors. Therefore, the versatility of the phase advance capacitor increases and the reliability of the system improves. Furthermore, since the harmonic compensator used in the present invention has a high-speed response, it is possible to suppress transient vibrations due to resonance between the inductance and capacitance of the power grid, which is caused by transient load fluctuations, etc. This can contribute to improving stability.

[Brief explanation of the drawing]

Fig. 1 is a power distribution system diagram in which a harmonic compensator is connected to explain an embodiment of the present invention, and Fig. 2 is a power distribution system diagram in which a phase advance capacitor is connected to explain the prior art. be.

Claims (1)

[Claims] A harmonic compensator is constituted by a static power converter including a high-frequency switching element and a control device, and the static power converter is connected to the power supply side of a phase advance capacitor provided in a power transmission and distribution system. An output terminal of the device is connected to the control device, and the control device detects harmonics contained in the reactive current flowing into the phase advance capacitor via a current detector provided on the power supply side further from the point where the output terminal is connected. A phase advancing capacitor characterized in that a wave component is extracted and calculated, and then, based on the calculation result, a harmonic current that cancels out the harmonic component is injected from the stationary power converter into the phase advancing capacitor. harmonic compensation control method.