Disclosure of Invention
Aiming at the defects of the existing ferromagnetic element no-load characteristic measuring method, the invention provides a ferromagnetic element no-load test by adopting a low-frequency power supply. As can be seen from E ═ 4.44fN Φ, the core saturation voltage of the ferromagnetic element is substantially proportional to the power supply frequency, and under the excitation of the low-frequency power supply, the power supply voltage can be greatly reduced, while the no-load current is substantially unchanged, so that the capacity of the test power supply can be reduced by times. And measuring the no-load loss, the no-load current and the harmonic characteristics thereof under the low frequency, and calculating the no-load loss, the no-load current and the harmonic contents thereof converted to the power frequency test condition according to a related algorithm, thereby achieving the purpose of replacing the power frequency test with the low frequency test. Tests prove that the method has better consistency with a power frequency test method directly adopted.
In order to achieve the purpose, the invention adopts the following technical scheme:
a low-frequency measurement method for no-load characteristics of a ferromagnetic element is characterized by comprising the following steps:
1. an equivalent circuit model of the open circuit on the high-voltage side of the ferromagnetic element is established, and is shown in figure 1. Wherein R isdcIs a direct current resistance on the winding, LσFor leakage inductance of the side winding, ReNonlinear inductor L with hysteresis loop for equivalent resistance of eddy current lossmFor exciting inductance, hysteresis loss PhIs contained in LmIn (1). i.e. iex(t) is an excitation current, im(t) is a flow through LmMagnetizing current of ie(t) is the eddy current loss equivalent current, u (t) is the excitation voltage applied to the winding;
2. the no-load loss of the ferromagnetic element is mainly core loss, and the core loss mainly comprises magnetic hysteresis loss and eddy current loss:
in the formula, PhAnd PeHysteresis loss and eddy current loss, respectively; ceDetermining the resistivity for the eddy current loss coefficient; chThe hysteresis loss coefficient and the material property are determined; b ismIs the peak value of the magnetic flux of the iron core; f is the frequency; v is the volume of the iron core; delta is the thickness of the silicon steel sheet; wh(W/Hz) and We(W/Hz2) Unit hysteresis and eddy current loss are generated for each magnetization period, respectively. Thus if B at different frequencies is guaranteedmIf they are consistent, W can be considerede、WhIs constant, and when the U/f under different frequencies is consistent in the test, B can be considered asmAre equal. W is determined by the core losses at two different frequencieshAnd WeA value of (d);
3. and (3) opening the high-voltage side of the winding, applying voltage to the low-voltage side, and recording voltage and current data when the U/f is equal under two different frequencies. Calculation formula of iron loss:
where u (t) is the voltage applied across the winding, iex(t) is the excitation current, IexIs its valid value;
4. calculating the corresponding iron loss under each frequency to obtain:
5. from equation (3), solving the equation can obtain WeAnd WhComprises the following steps:
6. thus, the iron loss at power frequency is translated:
wherein f isnA nominal frequency, typically 50Hz or 60 Hz;
7. iron loss current can be divided into hysteresis loss current and eddy current loss current:
in the formula IFe、Ih、IeFor effective value of corresponding current, from E to KvfNBmS, knowing that E is proportional to the frequency f, the eddy current loss current ieHysteresis loss current i proportional to the frequency first powerhIndependent of frequency. And because of B at different frequenciesmAre equal to each other, so that imAnd (3) equality, converting to the exciting current under the power frequency:
8. loss of current i due to eddy currentseProportional to the frequency first power, convert to the eddy current at power frequency:
Ien=Ie·fn/f (7)
9. as shown in fig. 1, since the eddy current contains only the fundamental component, it is only necessary to compensate the eddy current to the fundamental component of the excitation current when calculating the excitation current, and the phasor diagram is as shown in fig. 2, and is converted to the fundamental component of the excitation current at power frequency:
10. converting to exciting current under power frequency:
wherein, Iex(k)The current effective value of the kth harmonic wave under low frequency is obtained;
11. percent of no-load current harmonics:
K(k)the kth harmonic current accounts for the effective value of the fundamental current, and even harmonic content is the same as that of the fundamental current due to symmetrical positive and negative semi-axes of the waveformThis is zero. Therefore k is 1,3,5,7 …, k>1 hour, the amplitude of the idle current higher harmonic under low frequency and power frequency excitation is equal, i.e. Iexn(k)=Iex(k);
12. Converting to no-load loss at rated frequency:
13. because the voltage drop on the leakage inductance is very small and can be ignored when the leakage inductance is in no load, the leakage inductance is converted into the excitation voltage under the rated frequency:
Un=E·fn/f+Iexn·Rdc(12)。
thus, the excitation voltage U converted to power frequency can be obtainednThe corresponding relation between the power frequency excitation voltage effective value and the no-load loss, the excitation current and the no-load current harmonic content under the power frequency achieves the purpose of replacing the power frequency test by adopting a low frequency test.
Compared with the prior art, the invention has the following advantages:
1. the low-frequency sine wave power supply is adopted for testing, so that the capacity, volume and weight of the testing power supply can be reduced by times, the testing process is more convenient, and the cost is lower;
2. the testing voltage is reduced, the requirement on the insulation performance of the testing equipment is low, and the safety of testing personnel is guaranteed.
Detailed Description
In order to enable a person skilled in the art to better understand the technical solution of the present invention, the following will clearly and completely describe the technical solution in the embodiments of the present invention with reference to the accompanying drawings and the detailed description, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The measurement process is as follows:
fig. 4 is a schematic view of the measurement method of the present invention.
Step 100: according to the T-type equivalent circuit model, an equivalent circuit with one side (high voltage side) of the ferromagnetic element open is established, as shown in FIG. 1, wherein RdcIs a direct current resistance on the winding, LσFor leakage inductance of the side winding, ReNonlinear inductor L with hysteresis loop for equivalent resistance of eddy current lossmFor exciting inductance, hysteresis loss PhIs contained in LmIn (1). i.e. iex(t) is an excitation current, im(t) is a flow through LmMagnetizing current of ie(t) is the eddy current loss equivalent current, u (t) is the excitation voltage applied to the winding;
step 200: a schematic diagram of a measurement process of a preferred embodiment provided by the invention is shown in fig. 2, a high-voltage side is open-circuited, a low-frequency sine wave with 2 frequencies is applied to a low-voltage side (U/f is ensured to be equal under different frequencies), a data acquisition device records corresponding voltage and current data, and the iron core loss under each frequency is calculated according to a formula (2);
step 300: the unit hysteresis loss W in each magnetization period is calculated from the expressions (3) to (4)hAnd eddy current loss We;
Step 400: calculating the core loss P converted to power frequency according to the formula (5)Coren;
Step 500: calculating the eddy current I converted to power frequency according to the formulas (6) to (8)eFundamental component of exciting current Iexn(1);
Step 600: calculating the exciting current I converted to power frequency according to the formulas (9) to (10)exnAnd its harmonic content K(k);
Step 700: calculating the no-load loss P converted to power frequency according to the formula (11)n;
Step 800: calculating the excitation voltage effective value U converted to power frequency according to the formula (12)n;
Step 900: drawing PCoren-Un,Iexn-UnRelation curve, and K(k)-UnTable of harmonic content.
The foregoing are merely exemplary embodiments of the present invention, which enable those skilled in the art to understand or practice the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.