JPH03221886A - Method for measuring core loss - Google Patents

Abstract

PURPOSE:To accurately measure the core loss of a magnetic material even in a low power factor state by winding up the windings of a magnetic core coil and an air-core coil in the same direction on the primary side, winding respective coils in the mutually reverse directions on the secondary side and then connecting respective coils in series. CONSTITUTION:On the primary side for supplying power by using the air-core coil 7 in addition to the magnetic core coil 2, the primary windings (a), (c) of the coils 2, 7 are wound up in the same direction and connected to each other in series. On the secondary side for detecting voltage, the secondary windings (b), (d) of the coils 2, 7 are wound up respectively in the reverse directions and then connected to each other in series. Thereby, the absolute value of voltage E2 generated on the winding (b) is reversed to voltage E2' generated on the winding (d) and voltage E3 obtained by synthesizing the voltages E2, E2' is remarkably reduced and the phase of the E3 is almost the same as that of a primary current I1. Since I1.E3=E1.E2 is formed, the core loss can be accurately found out in a high power factor state by measuring I1.E3 instead of the measurement of I1.E2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for measuring iron loss, and is particularly suitable for measuring iron loss of a magnetic core material with low magnetic permeability.

[Prior art] Recently, demand for magnetic recording devices and switching power supplies has been increasing, but components such as transformers and coils account for high costs and have become important components in these products. . In order to design compact, low-loss transformers and coils, it is necessary to understand the iron loss characteristics of the magnetic core material.

Figure 4 shows the conventional iron loss measurement method. In the figure, 1 is a high-frequency voltage oscillator, and includes an amplifier for amplifying its oscillation output. The oscillator 1 energizes the primary winding a wound around the cored coil 2 to excite the magnetic core of the cored coil 2 . 3 is a resistor for current detection. The voltage generated across the resistor 3 and the voltage generated across the secondary winding are stored in the waveform storage W4 and processed by the computer 5.

Here, the iron loss W c (unit: W/m') per unit volume of the magnetic core of the cored coil 2 is expressed by the following formula.

In the above equation, N1 is the number of turns in the primary winding a, N2 is the number of turns in the secondary winding, ■ is the volume of the magnetic core, 11 is the current flowing in the primary winding a, El is the voltage across resistor 3, and E2 is the voltage of the secondary winding, and R is the resistance value of the resistor 3.

Further, T is the period of the oscillation waveform by the oscillator 1, and when the oscillation frequency is f, there is a relationship of T=1/f.

■The integral value of the equation is generally calculated by the computer 5, but instead of using the waveform storage device 4 and the computer 5, there is also a measurement method in which a multiplier voltmeter is used to integrate the voltage in an analog manner. be. Further, as a method for detecting the primary current (1), in addition to the method using the resistor 3, there is also a method using a current probe.

Furthermore, as shown in FIG. 5, a method has also been proposed in which the voltage E of the primary winding a is detected instead of the voltage E2 of the secondary winding 1. Since this method does not require the provision of a secondary winding, it is simpler than the above-mentioned method, but the loss including the copper loss due to the primary winding a is measured. Furthermore, as the oscillation frequency of the oscillator increases, 1
Since a phase difference may occur between the current flowing through the secondary winding a and the voltage E1 of the primary winding a, it has also been proposed to correct this using a computer (IEICE Information PE
86-27).

[Problems to be Solved by the Invention] The above-described iron loss measuring method is widely used, and measuring devices are also commercially available. When measuring the iron loss of a high magnetic permeability material such as ferrite, the measurement accuracy of the above-mentioned iron loss measuring method is relatively high, and the reliability of the measured value is high. however,
When measuring the core loss of low permeability materials such as gapped ferrite cores and some Das I-cores, it is known that measurement accuracy deteriorates under low power factor conditions. This is the ratio of I to the magnitude of II and E2 (for example, effective value).
This is because the value of 11E2dt per (1/T)S becomes extremely small at &, and the measured value may fluctuate depending on the conditions at the time of measurement and the calculation accuracy of the integral. Specifically, the resistance value of the resistor 3, the number of turns Nl of the primary winding a and the secondary winding)
, N2, the number of storage bits of the waveform storage device 4, etc.
The measured value of iron loss sometimes fluctuated.

As a method for accurately measuring iron loss under such a low power factor state, a method as shown in FIG. 6 (see IEE of Japan magnetis study group material MAG-88-178) has been proposed. In this method, a capacitor 6 that resonates at the measurement frequency is placed in series with the inductance of the primary winding a to make the phases of El and El almost the same, thereby reducing the power factor during measurement. It is something that we are trying to improve. The capacitance C of the capacitor 6 or the measurement frequency f of the oscillator 1 is set so that the relationship 2xf=1/(LC) is established, where the inductance of the primary winding a is the inductance and the capacitance of the capacitor 6 is C. With this method, it has become possible to accurately measure the iron loss of a gapped core.I7 However, this method can only be applied to the primary winding method, so the resistance of the primary winding a It is possible to directly measure only the loss that excludes the copper loss caused by the capacitor 6 and the loss caused by the capacitor 6. Therefore, there is a drawback that it is difficult to measure magnetic core materials with a small iron loss per unit current.

The present invention has been made in view of the above points, and its purpose is to provide an iron loss measurement method that can accurately measure the iron loss of a bow or magnetic core under a low power factor condition. 9 [Means for Solving the Problems] In the iron loss measuring method according to the present invention, as shown in FIG. 1, an air-core coil 7 is used in addition to the magnetic-core coil 2 to On the side, the primary winding a of the magnetic core (-1 coil 2) and the primary winding C of the air-core coil 7 are wound in the same direction and connected in series. On the other hand, the secondary winding (J) of the coil 2 (with magnetic core i=j) and the secondary winding (d) of the air-core coil 7 are wound in opposite directions and connected in series. Wind the primary windings a and C in opposite directions to create the secondary winding 1)
Similar results can be obtained by winding and d in the same direction. In this way, the voltage E2 generated in the secondary winding of the magnetic core coil 2 and the voltage E2' generated in the secondary winding d of the air-core coil 7 will be in opposite directions, and the voltage E2 that is the sum of these voltages will be
3 has a significantly smaller absolute value than E2, and the phase of E3 is almost in phase with the primary current 11.

Here, it is desirable that the dimensions of the air-core coil 7 and the number of turns N, ', N2'' of the primary winding C and the secondary winding d be designed so that E2+E2'' is as small as possible.

- As an example, assume that the dimensions of the air-core coil 7 are the same as those of the magnetic-core coil 2, and the number of turns N,' of the primary winding C is the same as that of the magnetic-core coil 2.
The number of turns N1 of the primary winding a is equal to N1, and the number of turns N2' of the secondary winding d is equal to the number of turns N1 of the primary winding a of
The number of turns is the number of turns N2 of 13 multiplied by the relative magnetic permeability. In other words, if the relative magnetic permeability of the coil 2 with a magnetic core is μmm, then N2
'-μrN2. In this way, the air core coil 7
The magnetic field excited by is the same as that of coil 2 with magnetic core,
The voltage E2. induced in the secondary winding 1), d. E,' are almost the same for the magnetic cored coil 2 and the air-core coil 7.

In Fig. 1, for ease of understanding, the primary winding a and secondary winding b of the magnetic core coil 2 and the primary winding C and secondary winding d of the air-core coil 7 are shown as split windings. However, in actual measurements, it is necessary to wind the primary winding and the secondary winding uniformly over the whole in order to reduce leakage magnetic flux. In addition, on the secondary winding side, the connection point S of the secondary windings S and d of the magnetic core coil 2 and the air-core coil 7 is connected to the waveform storage device 4 due to the secondary voltage of the magnetic core coil 2. By integrating E2 over time,
It is provided to measure the magnetic flux density B induced in the cored coil 2 at the same time as the iron loss Wc, and the above-mentioned wiring is unnecessary when measuring only the iron loss. Connection point S of secondary windings S and d
Even with a circuit configuration in which the waveform storage device 4 is not connected to the waveform storage device 4, it is possible to know the relationship between the iron loss and the magnetic field (current).

Further, an example of a measurement circuit using the primary winding method is shown in FIG. In this circuit configuration, the secondary windings s and d are omitted, and instead of storing the voltage E2E2'' of the secondary windings s and cl in the waveform storage device 4, the voltage EE1' of the primary windings a and e is stored. Memorize. Primary windings a and c are wound in opposite directions and connected in series. However, in this case, measure the loss including the copper loss due to the winding resistance of the magnetic core coil 2 and the air-core coil 7. I will do it.

[Function] The reason why the iron loss of the cored coil 2 can be measured accurately even at a low power factor when using the measurement circuit shown in Fig. 1 is explained in the third section.
This will be explained using the square diagram in the figure.

In the measurement circuit shown in Fig. 1, the primary currents flowing through the primary windings a and c, and the secondary voltages E 2 and E 2' generated in the secondary windings 1) and d are shown as vectors in Fig. 3. It is shown in Here, the iron loss We is expressed by the following formula.

We"" I, E2/V 111XIE2ICO3θ/V,, - ■ J in the above formula
3, ■ is the magnetic core volume, 11・E2 is the vector ■1 and E
The inner product of 2, III, 1E21 is the vector 1. , the absolute value of E2, θ is the angle formed by E2 and The current problem is that 5θ is close to 90 degrees, and the power factor is cos
This is a state in which θ is extremely small.

At this time, the inner load of vectors E1 and E2, ・E2, becomes smaller than the absolute values l111 and 1E21, and the iron loss Wc
The measurement accuracy will deteriorate.

On the other hand, in the air-core coil 7, although no iron loss occurs, in principle, the secondary voltage E2' of the air-core coil 7 and the primary current 1. The angle they make is 90 degrees, and the inner product of the vectors L and E2' is I+'E2""0. Here, if the wiring is arranged as shown in FIG. 1, the secondary voltages E2 and E2 will be in opposite directions. Therefore, as shown in FIG. 3, E3=E2+E2' is E
2. E2'', but the angle θ' between E and 11 is significantly smaller than θ, and the power factor cos θ' is larger than cO8θ.

Engineering 1/E3-1.・E2−+−I, ・E2■1・E2 Therefore, if you measure Xl・E3 instead of ■1・E2, it is possible to calculate the iron loss with high accuracy when the power factor cos θ' is high. becomes.

[Example] As an example of the method for measuring iron loss according to the present invention, the iron loss was measured using the measuring method of the present invention and a conventional method for a core HP-12 manufactured by Tokin. This magnetic core has a toroidal shape, an average magnetic path length of 52.degree. 15 mm, a cross-sectional area of 25.4 mm.sup.2, and a relative magnetic permeability of .mu.r-100. Frequency f-100kHz, excitation magnetic field Hm-800A/m,
Induced magnetic flux density B=0. Iron loss was measured under the conditions of IT and magnetic flux sine wave. In the measurement method of this example, an air-core coil having the same dimensions as the coil with a magnetic core was used, and the coil was wound so that its secondary voltage was almost the same as the secondary voltage of the coil with a magnetic core. The measurement results according to the conventional method shown in FIG. 4 are shown in Table 1, and the measurement results according to the present invention are shown in Table 2.

The unit of iron loss measurement is kW/m3. As is clear from the measurement results shown in this table, in the conventional method, the measured value of iron loss Wc changes greatly depending on the number of turns N, , N2, whereas in the measurement method according to the present invention, Number of turns N,
, N, N, °, and N2', the fluctuations in the measured values are slight, and it can be seen that the iron loss is measured with high accuracy.

Table 1 Table 2 [Effects of the Invention] In the present invention, as described above, in the method of measuring the iron loss of a magnetic core based on the inner product of the excitation current of a coil with a magnetic core and the winding voltage, The same excitation current as the coil with a magnetic core is passed through an air-core coil that has no iron loss, and the voltage and excitation current are obtained by combining the winding voltage of the coil with a magnetic core and the winding voltage of the air-core coil so that they have opposite polarities. Measure the iron loss of the magnetic core based on the internal bond 1? Therefore, it has the effect of making it possible to accurately measure iron loss in low power factor conditions, such as when measuring low magnetic permeability materials9.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a measuring circuit for implementing the measuring method of the present invention, FIG. 2 is a circuit diagram of another measuring circuit for implementing the measuring method of the present invention, and FIG. 3 is an operation of the present invention. Explanatory diagram, Fig. 4 is a circuit diagram of a conventional example, Fig. 5 is a circuit diagram of another conventional example,
FIG. 6 is a circuit diagram of another conventional example. 1 is an oscillator, 2 is a coil with a magnetic core, 3 is a resistor, 4 is a waveform storage device, 5 is a computer, and 7 is an air-core coil.

Claims (1)

[Claims] (1) In the method of measuring the iron loss of a magnetic core based on the inner product of the excitation current of the coil with a magnetic core and the winding voltage, the same excitation current as that of the coil with a magnetic core is passed through an air-core coil that has no iron loss, and the A method for measuring iron loss characterized by measuring the iron loss of a magnetic core based on the inner product of the excitation current and the voltage obtained by combining the winding voltage of the attached coil and the winding voltage of the air-core coil so as to have opposite polarities. .