SI24125A - A deviceand a method for esthablishing saturation of magnetic cores of transformators - Google Patents

Abstract

The method for determining the saturation of the magnetic core of a transformer is based on a measuring bridge with a coil. Based on the induced voltage in the measuring bridge coil, the saturation state of the transformer core can be determined. With a calibrated bridge, we can easily and directly obtain information about the density of the magnetic field in the core. Local or global saturations can be measured with a measuring bridge. The bridge is very flexible and easy. It also works well in areas with high electromagnetic pollution.

Description

APPARATUS AND METHOD FOR DETERMINING THE SITUATION OF MAGNETIC TRANSFORMERS

TECHNICAL FIELD

Electrical engineering; DC-DC converters; transformers; transformer cores

TECHNICAL PROBLEM

A technical problem solved by the object of the invention is the detection of the saturation of the magnetic cores of transformers, preferably in DC-DC converters. Those skilled in the art are aware that saturation of the magnetic core causes large current peaks, which can lead to malfunctioning, safety shutdown or even destruction of the device. Further, causes that contribute to the occurrence of magnetic core saturation, such as asymmetric structure, component variations, etc.

BACKGROUND OF THE INVENTION

The occurrence of magnetic core saturation is problematic especially in DC-DC converters. The saturation agents can be nonlinear semiconductor components and an asymmetric transformer structure [Gorazd article]. With a suitable meter and method, saturation can be prevented and the device will be able to function better and material to be used more efficiently. Existing saturation and measurement methods are based on:

• Measuring the magnetic flux of a fast-growing device in saturation (USPT 5942134) • An integrated magnetic flux meter measuring the magnetic density in the air gap (USPT 6532161 B2) in the air gap • Measuring the secondary current and mathematical model of the transformer (US 2005/0140352

Al) • additional transverse winding (US 4439822) • additional core (US3611330)

Those of skill in the art will be aware that the simplest methods based on integrating pressured or induced stress in the core are the simplest. The main disadvantage of these methods is that in order to determine the magnetic flux density, the voltage must be integrated. When integrating, there are various measurement errors, residual voltage of the operational amplifier, disturbances, etc. they lead to an incorrect result and in most cases such methods are useless.

The disadvantages of methods based on magnetic flux determination are generally due to the subtraction of secondary and primary currents, where the difference is very small. Due to meter errors, signal discretization, and possible interference, it is difficult to determine the magnetic flux correctly. Very good gauges are required.

Methods with built-in magnetic field sensors are expensive and poorly handled in the event of high environmental pollution. Given the inhomogeneous magnetic field in the nucleus, we also need to know the local saturation point.

Methods based on mathematical models, however, require the development of a good model, which must be extremely accurate. They also require high computing power and precise meters. Responsiveness is also a disadvantage.

In general, the problem of saturation detection is difficult because the magnitudes in the saturation field change very quickly, which requires very dense sampling of signals and an immediate response of the saturation suppression system.

DESCRIPTION OF THE NEW SOLUTION

The technical problem presented above The solution and method for determining the saturation of the magnetic cores of transformers is solved by simple determination of saturation by means of a measuring bridge (101) with a measuring coil (102). The bridge consists preferably of magnetically well conductive and electrically poorly conductive material (consequently fewer eddy currents which could adversely affect the operation) but also of other material. The bridge is preferably of semicircular shape with evenly spaced winding along the entire length of the bridge (111), but may also be of other shapes and configurations, e.g. (112). The shape, size and parameters of the bridge and the coil depend on the dimensions of the transformer and the location of the saturation. Important parameters of a bridge that can vary depending on the specific case are the cross-section of the bridge 121 (121), its mean length / _t (122) and the material of the bridge, since these determine the magnetic resistance of the bridge according to equation (1), where μο is permeability blank space and μι relative permeability of the bridge material. An important parameter of the measuring coil (102) is the number of envelopes N _t (123), since it affects the value of the induced voltage in the measuring coil «j _t by equation (2),“ u = d <t>, dl (2) where Φι is magnetic flow through the measuring bridge and the coil.

The principle of operation of the bridge is explained by means of Figure 2. Figure 2 shows a typical transformer with three windings for use in DC-DC converters. We attach the bridge to the transformer core (201), which can be of any shape and configuration. As the nucleus under the bridge (202) approaches saturation, the magnetic resistance increases rapidly. Due to the lower magnetic resistance of the measuring bridge above the core (203), more and more magnetic flux (204) begins to contract over the bridge past the core (205). As a result, the induced voltage in the winding starts

the bridge (206) rises steeply. Based on the rapid increase of the induced voltage in the measuring coil (208), we can deduce the saturation of the core under the measuring bridge.

A typical form of induced voltage in a measuring coil when the nucleus enters saturation is shown in Fig. 301. From the induced voltage response in the coil winding (301), we can deduce the saturation state in the magnetic core under the bridge when the induced voltage rapidly increases or decreases. it falls. Figure 301 shows that two typical peaks occur in each power half-life, (310) and (311). When the nucleus goes into saturation, the induced voltage increases and a voltage spike (310) is formed, and when the supply voltage is subsequently switched, a voltage spike of opposite polarity (311) appears due to the rapid decrease of the magnetic flux through the measuring bridge. The latter does not represent a state of saturation. Thus, two voltage peaks are obtained, at the beginning of the half-period (311) and at the end of the half-period (310). Therefore, for the unambiguous determination of the correct tip and the saturation point, we need an additional indicator to select the voltage tip at the end of the half-period (310), which can be obtained in several ways, preferably with an additional measuring envelope (210) in which to measure the induced voltage (211), which it is caused by magnetic flux in the nucleus. The form of this induced voltage is shown in (302). By integrating this induced voltage, we obtain an approximate course of the magnetic field density in the nucleus (303). We can then easily determine the correct pulse using a logic circuit, e.g. enable saturation detection to operate when condition (3) δΑ> θ P) is fulfilled and obtain (304). It is now easy to determine the saturation point when condition (3) is satisfied and when the induced voltage (301) reaches the desired value, e.g. (320) or (321). Instead of the induced voltage in the additional sheath, the additional condition can also be determined otherwise, e.g. we measure the voltage applied. The correct pulse can also be determined in other ways, such as. pulse polarity and pulse discharge in a measuring coil, using neural networks, etc.

By calibrating the bridge for certain operating conditions (for example, for the specified transformer pressured measured induced voltage at the bridge, determine the magnetic field density in the nucleus), the nucleus can also switch between arbitrary maximum magnetic field densities in the nucleus (± 2? _Sat ), eg between 331 or between 332.

• · · ·

In the case of a homogeneous magnetic field in the nucleus, a single bridge is sufficient to determine the saturation of the nucleus. However, the magnetic field in the transformer core may also be inhomogeneous and as a result, the saturation of the core occurs locally and even at different times. This may be due to structural nature (asymmetrically distributed transformer windings, etc.). In this case, any number of bridges can be used to determine saturation. We can also use the bridge to find the saturation point.

The advantages of the bridge are its simplicity and flexibility, as the cross section (121), the length of the bridge (122) and the coils of the measuring coil (123) can be adjusted to suit the specific situation. Saturation detection is also not computationally demanding. Saturation can be detected both at idle and on the transformer. Unlike other methods, local and global kernel saturation can be determined. The advantage is that by calibrating the bridge, we determine the saturation point ourselves and have information about how much saturation we have to deal with.

Claims (4)

PATENT APPLICATIONS A method for determining the saturation of magnetic cores by means of a measuring bridge with a coil, characterized in that the bridge (101) is restrained on the transformer core (201), which can be of any shape and configuration, with the core below the bridge (202) approaching saturation, the magnetic resistivity begins to increase rapidly, and further, due to the lower magnetic resistance of the measuring bridge above the core (203), more and more magnetic flux (204) begins to conclude across the bridge past the core (205) and consequently the induced voltage in the winding of the bridge (205) begins. 206) increase steeply, and finally, based on the rapid rise of the induced voltage in the measuring coil (208), we can deduce the saturation of the nucleus under the measuring bridge. Method according to claim 1, characterized in that the saturation of the transformer core is determined on the basis of the induced voltage in the winding of the measuring bridge and an additional criterion such that when the core goes into saturation, the induced voltage is increased and a voltage tip (310) is formed when consequently, we switch the supply voltage, and due to the rapid decrease of the magnetic flux through the measuring bridge, a voltage pole of opposite polarity (311) appears, the latter not representing the state of saturation, thus two voltage peaks are obtained, at the beginning of the half-period (311) and at the end of the half-period (310 ). 3. A device for determining the saturation of magnetic cores by means of a measuring bridge, characterized in that, based on the induced voltage in the winding of the measuring bridge, it determines the saturation of the unidirectional component of the magnetic field in the nucleus and, by guiding the converter for generating pulse width modulated supply voltage of the primary winding can also be adjusted to the desired value. Apparatus according to claim 4, characterized in that the bridge consists preferably of magnetically well conductive and electrically poorly conductive material (consequently less eddy currents which could adversely affect the operation), further that it is preferably semicircular the spaced windings along the entire length of the bridge (111) and the shape, size and parameters of the bridge and the coil depend on the dimensions of the transformer and the saturation point, with important bridge parameters that may vary depending on the specific case being the cross section of bridge A _t (121), its mean length / _t (122), and the bridge material.