JPH0336284B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a harmonic low impedance transformer that reduces distortion of the output voltage waveform.

Recently, more and more loads are being controlled by switches using thyristors. For this reason, a large harmonic current flows through the transformer supplying power to the load, causing a large voltage drop, and this voltage drop due to the harmonics greatly distorts voltage deformation. As a result, it not only adversely affects the phase advance capacitors and control equipment connected to the load side, reducing the quality of the supplied power, but also affects loads (power consumers) that are not the source of harmonics. The effects of this have spread, creating an unfavorable situation in terms of power supply. In order to explain such a state, FIG. 1 shows a simplified equivalent circuit of a conventional transformer. In this equivalent circuit, if the resistance is R, the inductance is L, and the angular frequency is w, the voltage drop E〓 _T when an alternating current I〓 flows is E〓 _T
= I〓R + jwL), and it can be seen that the voltage drop E〓 _T increases as the frequency increases.

The present invention reduces the distortion of the output voltage waveform even when the input voltage contains harmonics by lowering the excitation impedance (hereinafter also simply referred to as impedance) of the transformer with respect to harmonic components of the input voltage. The present invention provides a harmonic low impedance transformer that can perform

In order to achieve the above object, the present invention connects a shunt core around which a tertiary winding is wound to a closed magnetic circuit core around which a transformer winding consisting of a primary winding and a secondary winding is wound. By forming a magnetic bypass and connecting a capacitor to the tertiary winding, a filter function for harmonics is provided. That is, the magnetic flux due to harmonics in the closed magnetic circuit iron core is made to reach a minimum value at a specific resonant frequency of the parallel resonant circuit formed by the tertiary winding and the capacitor, thereby lowering the impedance of the transformer against harmonics. It's a diagram.

The harmonic low impedance transformer of the present invention will be explained in detail below with reference to the drawings.

FIG. 2 is a side view of one embodiment of the present invention,
In the figure, 1 is a transformer winding consisting of a primary winding and a secondary winding concentrically wound around a square-shaped closed magnetic circuit core 2, and 3 is a transformer winding consisting of a tertiary winding 4. This shunt core 3 is a U-shaped shunt core, and each end of the shunt core 3 is joined to the side surface of the closed magnetic circuit core 2 via spacers 5, 5 made of, for example, paper and having an appropriate thickness. A magnetic side path is formed in the closed magnetic path iron core 2. In order to maintain the joined state, these two iron cores 2 and 3 are actually assembled integrally using assembly fittings (not shown). 6 is a capacitor, and this capacitor 6
Both terminals 6a, 6a are connected to both ends of the tertiary winding 4 by lead wires 7, 7. That is, 3
A resonant circuit is formed by the secondary winding 4 and the capacitor 6.

a closed magnetic path iron core 2 around which the transformer winding 1 is wound;
Shunt core 3 and tertiary winding 4 around which tertiary winding 4 is wound
The equivalent circuit of the harmonic low impedance transformer consisting of the capacitor 6 connected to the . where l ₁ , l ₂ and l ₃ are the leakage inductances of the primary, secondary and tertiary windings 4 of the transformer winding 1, respectively, and r ₁ , r ₂ and r ₃ are the leakage inductances of these windings, respectively. L ₁ , L ₂ and L ₃ are the inductances generated by the yoke 2a of the closed magnetic circuit core 2, the core leg 2b where no winding is wound, and the shunt core 3, respectively, and R ₁ , R ₂ and R ₃ are resistance components that can be seen as being connected in parallel to the inductances L ₁ , L ₂ and L ₃ , respectively. Here, the leakage inductances l ₁ , l ₂ and l ₃ are extremely small compared to the inductances L _{1 , L 2 and L 3 and} can be approximately ignored. and transformer winding 1 (primary and 2nd
Consists of the following windings. ) The frequency characteristic of the impedance of this harmonic low impedance transformer at no load is as shown in FIG. here
f ₁ is the parallel resonance frequency between the tertiary winding 4 and the capacitor 6, and f ₂ is the series resonance frequency between the transformer winding 1 and the capacitor 6.

Therefore, by matching this frequency f ₂ to the frequency of the harmonic to be suppressed, this frequency
The transformer impedance to f ₂ can be made extremely small, and harmonics of this frequency can be effectively suppressed. However, since there is loss in the actual circuit, the impedance value will not be completely zero, but it can be approximated to zero.

Furthermore, if the frequency f ₁ is selected to be close to the fundamental frequency, the impedance at the fundamental frequency can be increased. FIG. 5 shows the actual measurement of the relationship between frequency and impedance using such a harmonic low impedance transformer. As is clear from Fig. 5, the impedance of the transformer decreases rapidly as the frequency increases from the fundamental frequency (60Hz).
It reaches a substantially minimum value at the fifth frequency.

In conventional transformers, the impedance of the transformer increases slightly as the frequency increases, but in the harmonic low impedance transformer of the present invention, as the frequency increases, the impedance increases rapidly toward the resonant frequency, as shown by the curve in Figure 5. The harmonic suppression effect becomes noticeable. In addition, in the harmonic low impedance transformer of the present invention, a closed magnetic circuit core around which a transformer winding 1 consisting of a primary winding and a secondary winding is wound, and a shunt core around which a tertiary winding 4 is wound. 3 to form a magnetic bypass, and the tertiary winding 4
Since capacitor C is connected to , when viewed from the input side of the transformer, inductance L ₂ and capacitor 6 become in a series resonance state for a specific harmonic frequency, that is, the tertiary winding The impedance of the transformer is reduced by shorting the line to the harmonics. On the other hand, with respect to the fundamental frequency, when viewed from the input side of the transformer, the inductance _L3 and the capacitor 6 are in a parallel resonance state, and the impedance with respect to the fundamental frequency increases. As a result, as the frequency of harmonics approaches the resonant frequency of the series resonant circuit, the inductance of the transformer against harmonics is significantly reduced, reducing the voltage drop caused by harmonics and supplying high-quality power with less waveform distortion to the load. can do.

FIG. 6 shows another embodiment of the present invention, in which the same components as those in FIG. 2 are given the same reference numerals and their explanations will be omitted. In this harmonic low impedance transformer,
Primary winding W ₁ is installed in the left and right core parts of the closed magnetic circuit core 2.
and a secondary winding W ₂ are wound, respectively, and a shunt core 3' is connected to the upper and lower core portions via spacers 5, 5. A tertiary winding 4' is wound around the shunt core 3', and both ends of the tertiary winding 4' are connected to both terminals of the capacitor 6.
Therefore, the harmonic low impedance transformer shown in FIG. 6 also has the same function as the transformer shown in FIG. 2, and can obtain the same effects.

In particular, when a magnetic shunt is formed by winding a tertiary winding around a shunt core and joining the shunt core to a closed magnetic circuit core as in the present invention, the inductance _L3 can be easily reduced. Adjustability simplifies transformer design.

That is, in designing the transformer of the present invention,
It is necessary to reduce the excitation impedance for harmonic components, but in order to prevent the excitation current from increasing for the fundamental wave (50Hz or 60Hz), it is necessary to make the excitation impedance as large as possible for the fundamental wave.

In order to minimize the excitation impedance at harmonics (angular frequency Wf ₂ ), it is necessary to cause series resonance between L ₂ and the capacitor 6 (its capacitance is C) in FIG. 3. The condition is that if R ₂ is ignored, w _f2 = 1/√ ₂ ...(1) Here, L ₂ is the inductance caused by the core leg 2b where the winding is not wound as described above, and the adjustment Therefore, in order to satisfy the above conditions, it is necessary to adjust the capacitance C of the capacitor 6. That is, the capacitance C of the capacitor 6 is determined in order to reduce the excitation impedance to harmonics.

On the other hand, in order to minimize the excitation current for the fundamental wave, it is preferable to maximize the excitation impedance for the fundamental wave. If R ₃ , l ₃ and r ₃ are ignored in Fig. 3, the inductance L ₃
When the capacitor 6 and the capacitor 6 resonate in parallel, the excitation impedance becomes maximum. Angular frequency of fundamental wave w _f1
The condition for parallel resonance is w _f1 = 1/√ ₃ ...(2) Since the capacitance C of capacitor 6 has already been determined, in order to satisfy the condition of equation (2) at the fundamental frequency, It becomes necessary to adjust the inductance _L3 .

As in the present invention, when the tertiary winding 4 or 4' is wound around the shunt core 3 or 3' and the capacitor 6 is connected to the tertiary winding, the shunt core and the closed magnetic circuit core are The inductance _L3 can be adjusted appropriately by adjusting the magnetic resistance between the two.

For example, in each of the above embodiments, by changing the thickness of the spacer and adjusting the gap between the closed magnetic circuit core and the shunt core, the magnetic resistance between the closed magnetic circuit core and the shunt core can be changed. let inductance
L ₃ can be finely adjusted. Furthermore, by adjusting the facing area of the shunt iron core and the closed magnetic circuit iron core, the inductance L ₃ can be finely adjusted to satisfy equation (2).

As described above, according to the present invention, a magnetic shunt is formed by providing a shunt core around which a tertiary winding is wound around a closed magnetic circuit iron core around which a transformer winding is wound, and a capacitor is attached to the tertiary winding. Since the resonant circuit is connected, the resonant circuit functions as a filter against harmonics, and the impedance against harmonic components contained in the input voltage can be rapidly reduced. As a result, even if the input voltage contains harmonic components, it is possible to increase the voltage drop at the transformer, reduce distortion of the output waveform, and supply high-quality power to the load, which has an industrial effect. big.

Further, according to the present invention, a magnetic bypass is formed by winding a tertiary winding around a shunt core and joining the shunt core to a closed magnetic circuit core. By adjusting the gap between the shunt core and the closed magnetic circuit core, and by adjusting the facing area between the shunt core and the closed magnetic circuit core, the conditions for increasing the excitation impedance for the fundamental wave component can be finely tuned. Can be adjusted. Therefore, it is possible to easily design a transformer that suppresses an increase in excitation current relative to the fundamental wave component and also reduces distortion of the output voltage waveform.

[Brief explanation of the drawing]

Fig. 1 is an equivalent circuit diagram of a conventional transformer, Fig. 2 is a side view of an embodiment of the present invention, Fig. 3 is an equivalent circuit diagram of the transformer according to the embodiment of Fig. 2, and Fig. 4 is a diagram of the present invention. FIG. 5 is a curve diagram showing impedance characteristics versus frequency for the transformer of the invention. FIG. 6 is a curve diagram showing impedance characteristics versus frequency for the transformer of the invention. FIG. 6 is a transformer showing another embodiment of the invention. FIG. 1...Transformer winding, 2...Closed magnetic circuit core, 3, 3'...
Shunt core, 4, 4'... tertiary winding, 5... spacer,
6...Capacitor.

Claims (1)

[Claims] 1 A shunt core around which a tertiary winding is wound is connected to a closed magnetic path core around which a transformer winding consisting of a primary winding and a secondary winding is wound, and a magnetic shunt is created by the shunt core. 1. A harmonic low impedance transformer, characterized in that a capacitor is connected to both ends of the tertiary winding.